Check out the Fallout New Vegas version of this mod: https://www.nexusmods.com/newvegas/mods/69078
Free batch DDS converter https://www.nexusmods.com/fallout4/mods/46817

If your loading screen slide animation is broken, or you're only getting the main menu image when loading anywhere, then you should install my Broken Loading Screen Slide FIX Note: this DIY mod does not mess with the slide animation, but there are other mods that do. I made a fix after a mod broke my loading screens >:(

I made a mistake in the mod where FORM ID ExtraLoadScreenz213 was skipped when I was making the mod in the GECK, so image ExtraLoadingScreens\213.dds will not load in the original plugin. Sorry :(
But the new 999ExtraLoadScreenz plugin I made with my mod generator should have all 999 loading screen IDs, so update to that one :)

Update: NEW DIY LoadScreen Generator v0_3 WIP
Extended the script limitations, you can now generate up to 65,530   It turns out the actual limit is 63,488 IDs due to the engine limitation where IDs start at HEX 08 00 or 2048. So don't generate more than 63,488 IDs. I can probably extend the limit to FF FF FF or 16,777,215-2048= 16,775,167 unique IDs, but that would just be silly no? you can now generate mods with up to 63,480 unique loading screenz *O*, with custom FORM ID names and custom folder locations for the DDS images, all done in a user friendly command line interface. Update changes listed in the changelog.

The load screen generator is a proof of concept/prototype mod generator I made after a whole day of non stop coding. I've had this idea for a while now and didn't think it was possible, I originally planned to just make a small script that renames the IDs of the existing plugin with a simple command but it turns out it isn't that simple...

Still the scripts/mod generator works and can theoretically be used to easily make different loadscreen/wallpaper mods.

I'm mainly going to use this to organize my load screen images in seperate folders and merge the generated plugins/IDs by copying them as new
records into my existing merge patch so these small plugins don't take up that precious load order space.

999ExtraLoadScreens.esp can now let you add NINE HUNDRED AND NINETY NEIN LOAD SCREEEENZ
If you don't want this mod to spend any plugin spaces in your load order you can always zmerge the plugins or copy them as new records into another existing.esp (usually your merged patch esp) with FO3/xEdit (look at relevant screenshot for more info)

- You don't need to mess with GECK to use this mod, that's only if you want to create newloading screen ID's or change the image location of the existing  loading screens. Also ignore the Fallout New Vegas refrences in the images, I was too lazy to make new images for fallout 3 ;p

BTW, if you want some lore friendly wallpaper for your loading screens there are thousands of images up on the nexusmods media section:
https://www.nexusmods.com/images/recentlyendorsed/
https://www.nexusmods.com/newvegas/images/
https://www.nexusmods.com/fallout3/images/
https://www.nexusmods.com/fallout4/images/
https://www.nexusmods.com/skyrimspecialedition/images/
https://www.nexusmods.com/skyrim/images/
https://www.nexusmods.com/oblivion/images/
https://www.nexusmods.com/morrowind/images/
However you will have to convert them to DDS to use them in game, you can open the images with paint.net and save them as DDS (BC3 DXT5, don't enable mipmaps for the load screens to reduce the file size)

Saving the DDS as B8G8R8 (RGB 8?) Linear reduces the format artifacts and looks better than DXT5, however it also makes a
larger file size. You may want to look into a more optimized DDS compressor that looks better than DXT5 and doesn't use too much space.
DDS Optimizer Textures (Ordenador) https://www.nexusmods.com/skyrim/mods/12801
This modder says R5G6B5 was 99% close to the original.

- This will not mess with the vanilla load screens, so at first it may appear that nothing has changed when you see the normal load screens but
depending on how many custom loadscreens you're using they'll show up eventually. I recommend getting a loadscreen replacer if you get tired of the vanilla loadscreens.

- When looking at the screenshots, make sure to click that little square at the bottom left of the screen to hide the image view UI that's blocking part of the instructions.

- I made a PNG to DDS Batch converter for Texgenpack, link at the bottom of the description.
- Leave a coment if you would want more versions. Requests/Criticism welcome but not required ;p
- Before using the Bulk Rename Utility make sure you backup your images as it Irreversibility changes the file names.
- If you are using JIP NVSE, make sure "bLoadScreenFix=0" or you won't get random load screens. File location "\Data\NVSE\plugins\jip_nvse.ini"

[Quick Q&A]
Q: What is this mod?
A: It's just a simple esp with unique load screen FORM/Object ID's so you can customize your load screen :D

Q: Cool but y?
A: Well I was looking for a way to add my own custom load screens, but
there's little to no information on how do so and while there are other
non replacer mods that do add more load screens, I found it strange that
there were no templates or tutorials for noobs like me to make their
own custom load screens.

Install:
Just manually drag & drop the files to the "Data" directory of the game & enable the esp.
There should be a folder named either "CustomLoadingScreenz" (if you use the CustomLoadScreenz.esp) or "ExtraLoadingScreenz" (if you use the 999ExtraLoadScreenz.esp) in "Data\Textures\interface\loading"
Just fill the folder up with DDS images, preferably with the same aspect
ratio as your monitor, the images have to be renamed to numbers starting
with 001.dds up to however many IDs you're using.  CustomLoadScreenz200.esp for example will only allow up to 200.dds
While 999ExtraLoadScreenz.esp will allow UP TO 999.dds, however all the load screen ID's need to be
filled up, if you don't have enough images to fill up all the ID's you
can delete the numbers not being used with FO3Edit/xEdit (Example shown in the
screenshot) If you don't want to delete the load screen IDs (in case you're planning on adding more images later) you can make duplicate copies of an existing DDS image and just rename them to the missing numbers, this will consequently increase the chances of that same image appearing.

Sorry about the silly/cringy naming, but at least the name ID's are unique :p

 -------------------------------

Instructions/Explanation:

As an explanation, for the optional example images, I have only included 6
images (in game screenshots I made) because I'm too lazy to make 100
original works of art :) , they are located in this directory
"Data\Textures\interface\loading\CustomLoadingScreenz"
And have the following file names:

001.dds
002.dds
003.dds
004.dds

[005.dds to 049.dds if missing/left empty will show up as pink load screens
unless an image fills its place or the load screen FORM ID is removed
(tutorials in screenshots)]

0050.dds - File will not load because it's supposed to be named "050.dds"

[051.dds to 099.dds if missing/left empty will show up as pink load screens
unless an image fills its place or the load screen FORM ID is removed
(tutorials in screenshots)]

100.dds

If you want more images you will have to either make your own or download wallpapers/images others have made.
ALL IMAGES MUST BE DDS!!!! PNG'S, JPEGS, ETC... MUST BE CONVERTED TO DDS AND RENAMED/NUMBERED
I made a DDS Batch converter for Texgenpack, link at the bottom of the
description. It's a slow converter as it compresses the images though.

The way this mod/load screens in the game work is, there is an individual
"Load Screen" FORM ID for each image, starting from 001.dds (for this
mod) counting all the way up to 100.dds [001.dds, 002.dds, 003.dds
,004.dds... 100.dds] for this mod these images are in this directory
"Data\Textures\interface\loading\CustomLoadingScreenz\"
So it will only work if the images are there, moving or renaming the images will
obviously prevent the game from loading/finding it, but the loadscreen
in the mod will still be there looking for the image (resulting in a
pink loadscreen texture if it can't find it.)

Therefore the only thing you have to do is fill up the "CustomLoadingScreenz" folder with
100 DDS images, however they have to be renamed/numbered from 001 all
the way to 100 or else the mod won't be able to find the images. You can
use the "Bulk Rename Utility" program to rename/renumber multiple
files, see screenshot left in this mods mod page for a quick explanation
how. Links to the software left at the bottom of the description.

Using simple free software (that I have left links for at the bottom of the
description) , you can easily make your own collection of load screens.
While most of the other mods are only image replacers for the ~40 backgrounds
there are in the game, this mod will let you "add" (not replace) 100
additional loadscreens for you to personalize your own loading
experience. Note, the original vanilla load screens will be untouched, I
recommend to use a replacer mod if you get tired of the vanilla ones)
If you only have a certain amount of loadscreens you want to use, say 50,
21, 69, etc instead of 100, you can just delete the additoinal
loadscreens not being used with FNVEdit (example how to shown in
screenshot in this mods mod page)

For more advanced users:
If you have more than 100 images that you would like to use or don't want
to rename your images, or make seperate folders for your images, you can
open this plugin or any other plugin via GECK and edit/create your own
load screens, it's really simple. Just right click and edit a load
screen (recommend "GeneralLoadScreen01") and give it a new unique ID
(chaning an objects ID in GECK allows you to save it as a new object),
select your own custom image (which should be located inside the
"Data\Textures\" directory then either delete or edit the text in the
bottom box (I just leave it emtpy.)

This mod is also merge compatible as it only adds some simple FORM ID's, you can use FNVEdit to
select the whole loadscreen section in this plugin and copy it as a new
record into any other plugin. Just click ok (and not cancel) on the 5
prompt boxes and save it in any other plugin you want (preferably in
your merged patch plugin) you can then delete this mods plugin to save
on load order space. Don't worry about the ID conflict warning, as long
as you delete this mods plugin after merging/copying the loadscreen ID's
you won't have any problems.

It's also zMerge compatible for those who prefer this method:
https://github.com/z-edit/zedit/releases
Warning, merging plugins is for advanced users and can break or glitch your game.
Manual conflict corrections through xEdit before merging plugins is HIGHLY recomended.
Only merge simple plugins. Script heavy, MCM supported, UI, or ESM plugins are not merge friendly.

 -------------------------------

Uninstall:
Just delete the "CustomLoadScreenz100.esp" (or whatever it's called) as well
as the "CustomLoadingScreenz" folder where the images are, located in
"Data\Textures\interface\loading"

 -------------------------------

Free Software Links:

FNVEdit/xEdit
https://tes5edit.github.io/

Free program to rename miltuple files.
https://www.bulkrenameutility.co.uk/

Simple DDS viewer w/ batch converter from DDS to JPG/PNG/BMP but cannot convert to DDS unfortunatly.
https://www.bandisoft.com/honeyview/

Free ZIP & 7z Archive Manager
https://www.bandisoft.com/bandizip/

DDS image editor + converter (technically a converter since you can open
any supported image like a PNG and save it as DDS, however not a batch
converter)
https://www.getpaint.net/index.html

[Advanced Users]

Batch File I made for Texgenpack, a DDS converter:
FREE DDS Batch Converter for Texgenpack (WIP)

Which requires Texgenpack (CMD program, tutorial in the mod page for the link above):
https://github.com/hglm/texgenpack/releases

You will also need "pthreadVC2.dll" from here
ftp://sourceware.org/pub/pthreads-win32/prebuilt-dll-2-9-1-release/dll/x86/

DLL Source (in case the link above does not work):
https://sourceware.org/pthreads-win32/

The Texgenpack has a readme and opening the exe via CMD gives out simple command instructions.
But I made a tutorial on my simple Texgenpack batch DDS converter utility


[Copy Restrictions]
This isn't really that important to me, nor do I care much about this mod.
You're free to mess with and make your own versions of this mod, as well as share/upload it.
Just don't break any laws/copyright infringements like reuploading others people work or what not

BTW this is the first mod I've ever uploaded to the public, I apologize in advance for how "jank" it is so to speak.
I'm not sure what else there is for me to say or mention, so happy modding I guess :D