I'm planning on building a 3D game with 2D sprites like this: https://www.reddit.com/r/godot/comments/mcqzwc/almost_perfect_pixel_perfect_25d_pixelart_demo/

I want to do lighting with normal maps and LUTs like this: https://www.gamasutra.com/blogs/SvyatoslavCherkasov/20181023/329151/Graveyard_Keeper_How_the_graphics_effects_are_made.php

I know you can attach normal maps to 3D textures in Godot, but I'm new to game development in general and am wondering if something like this will be totally doable in Godot or if I should consider using Unity or Unreal?

I do not see why this wouldn't be doable. You can attach normal maps to textures in 3D with Godot, that's how PBR rendering works and expects. I'm not sure if the Sprite3D/AnimatedSprite3D node can take a normal map by default, but you could either write a shader to do this, or use a MeshInstance node with a quad and then apply the normal map there.

2 years later