Flame Blade leaves a lot to be desired. While Larian improved it from it's tabletop version by removing concentration and allowing it with two-weapon fighting, it seemed like the spell would have more synergy with other passive features. Unfortunately, the ideal passives don't synergize with it.

This mod makes some changes to Flame Blade making it behave more like a magically conjured scimitar.

• Now is a melee weapon attack that uses your spellcasting ability modifier for the attack rolls, like with the Melee Caster passive of the Sylvan Blade or Infernal Rapier.
• Can proc passives and features that require a melee weapon attack like Sneak Attack and Arcane Synergy (but will no longer proc passive features that require a spell attack like Arcane Acuity).
• Benefits from passives and features that require a melee weapon like the Dueling fighting style, Eldritch Knight's Weapon Bond, and Bind Pact Weapon (may also want a mod that makes it last longer like Spells Enhanced - Flame Blade loaded after this mod). 
• Adds the weapon actions Lacerate and Flourish if proficient in scimitars. Remember these are only available in your main hand, though there is a mod that changes that.
  

Everything else remains the same as vanilla, such as no ability modifier to damage. This should make it at least more synergistic with gear and multiclassing in gish builds and more appealing considering just how many good magic weapons are in the game, without going overboard.

Alternate version adds modifier to damage rolls like a normal main handed weapon and matches the 2024 PHB updated description (adds spellcasting modifier to damage and upcasting now scales every 1 level).

Install only 1 file using BG3 mod manager. Should work on existing saves without the need to long rest or respec. Can uninstall without breaking save files. Shouldn't conflict with mods that don't edit Flame Blade.

• As of version 1.1, I've attempted to make this compatible with the Long Rest and Ritual versions of Spells Enhanced - Flame Blade. Load my mod before (above) it.
  

I'll update the mod if I ever figure out how to make it behave as both weapon and spell attacks for maximum gish synergy, or figure out how to incorporate the Draconic Sorcerer Elemental Affinity: Damage - Fire.

Recommended mod: Multiclass Preferred Casting Ability Fix so that you can more freely build around your desirable ability. 

See my other spell mods:

• Infestation - 5e cantrip
• Melf's Acid Arrow AOE
• Poison Spray is Cone
• Metamagic Extended - Seeking Spell Cost Reduction
  

References and special thanks to:

• Let's Play with Fire Wiki
• Modding a custom class in 10 minutes or less
• Larian Export (LSLib) Tool
• BG3 Mini Tool
• Baldur's Gate 3 Modder's Multitool
• D&D 5e
• My TTRPG friends