You might want to have a look at Voxatron[1], the 3D version of Pico-8, that you get as a bonus when you buy a license of Pico-8.
Polygonal 3D is a huge step compared to 2D engines. You can't just create assets with a simple bitmap editor, you need to learn 3D modeling and it's a huge can of worm. And then you need to learn to animate your models...
With voxels you can just sculpt your models minecraft-style, it's a lot more intuitive I think. And animations could be done like for sprites: you just key your animations with different 3D voxel models.
I would also absolutely love a very simple N64/Saturn/PS1 era 3D modelling / game engine in such a lovely simple package.
Low-poly, low-res textures, with an option for that wonderful grainy kinda PS1 dithering if we'd want. :)
Unity shader asset: https://assetstore.unity.com/packages/vfx/shaders/psxeffects...
Godot shader example: https://github.com/MenacingMecha/godot-psx-style-demo
You can use modern modeling tools with self-imposed limits on model complexity and texture sizes. (Blender is even era-appropriate — its first public release was in 1998.)
In the context of a PS1-era demake: https://www.gamesradar.com/heres-how-to-create-a-ps1-demake-...
Alternatively, see Crocotile3D, which approaches that era's aesthetic from a different angle of simplified tile-based modeling: http://www.crocotile3d.com/