If you look at my profile you can see I upscale a lot of stuff and info, blah, blah.
Someone had requested this so here it is. Maybe worth it just for the doors, because that is something you run your face into all the time. :)

This:
I upscaled textures of Arri's Snow Elf Ruins Retextures and Chantry College of Winterhold  with ESRGAN models. On request. 

Is this a flawless masterpiece?
No, this is something my computer did while I did stuff because computer smart.

Kartoffel, does this really need to be 4x?
Sure why not? I recommend 2x for this, because original is already 2k.

Requirements:
Skyrim Special Edition - wow

Actually doesn't require these since it replaces. But still, here is the sauce:
Chantry College of Winterhold - as expected
Arri's Snow Elf Ruins Retexture Special Edition - big shock

Process:
All textures:   Remove BC1-3 compression with Bc1-smooth2 model.
Option A:Process with fatality-deJPG-ultra model.
All textures:   Upscale 4x with misc model.
All textures:   Compress to BC7.

Resolution:
4x: Max image resolution is 8k.
2x: Max image resolution is 4k. Recommended
1x: Just cleans the artifacts.

Types:
A: Is stylized slightly to produce more marble-like effect. Process : BC1-smooth2 -> fatality-deJPG-ultra -> 4xmisc
B: Identical to original. Process: BC1-smooth2 -> 4xMisc_4x_Deviance_interp_05.pth
ASSERUT: Arri's Snow Elf Ruins Retexture Upscaled Textures
CCOWUT: Chantry College of Winterhold Upscaled Textures

Difference of block compression BC1, BC3, and BC7:
In dds texture (the textures skyrim uses), compression via BC1, and BC3 (with alpha), is blocky. Because of this, in original Skyrim, people sometimes leave textures uncompressed. Uncompressed has a big file size. 
With the new block compression, via BC7, it is nearly the same quality as uncompressed, but has the same size as BC1, and BC3. However, this is only supported in Fallout 4 and Skyrim SE.
So even If I do not upscale, by removing BC1-BC3 artifacts and compressing as BC7, the quality is improved.
TLDR: Even without upscale, there is big difference. NO MORE BLOCKY! @400% zoom, so you can see the difference.


Compatibility:
Cannot use with Skyrim Legendary. See "Difference of block compression" above. If you change this BC7 -> uncompressed or BC1, BC3; then, it will work. Use Cathedral Assets Optimizer.

Permissions:
I don't care.

Credits:
ClstlDrmr83; Chantry College of Winterhold
arrioch;  Arri's Snow Elf Ruins Retexture Special Edition
xinntao; ESRGAN
Honh / ptsruder; image enhancing utility
Alsa; Models
Twittman; Models
BlackScout; Models
Game Upscale Discord and Wiki