Spent the day with Godot 4.0. It looks promising, but there are some pretty huge issues right now. Texture filtering seems completely busted on any setting. Meaning even 8K textures look low res and pixelated. Mip mapping only sort of works, but you need to create a new material from scratch. Meaning if you convert a 3.x project, none of the textures will have mip mapping, even if you reimport the texture. You have to create a new material for each material in the project.
Global illumination looks nice, but has artifacts. It's worse with SDFGI but also happens with VoxelGI. Basically there are these blob spots on the wall. It is not so obvious at far distance, but close up you can see them shimmering and flickering, especially with camera movement. There are rectangle artifact glitches all over the screen. Not sure why.
Objects seem to have some sort of metallic specular lighting, even with everything set to zero. Meaning objects that should be diffuse (like cloth) look like porcelain. The sky box rotates in the opposite rotation of the camera, which is sickness inducing. I tried to enable Basis Universal texture compression and the editor crashed, and now my project I spent all day on won't open.
Probably some other small stuff, but that is quite a lot of basic functionality broken. I'm not even going to attempt to make a demo in 4.0 in this state. I'm going to stick with 3.x for the time being, but I'll spend tomorrow writing bug reports for everything I discovered.