Been happening to me as well. I can run it through Proton instead but there is a notable performance hit.

Hey, that is an odd one. Really looks like the ground textures just didn't load in. Are you on the native version or by compatibility version are you doing proton/wine? Do you have a compositor running in your DE? My first bet would be vaidating the files through steam if thats how you own it, but I imagine you've tried that. Hopefully with some more details someone could help you

since proton experimental works better (as in, works, but bad performance), are you on a distro which has proton-ge-custom available? Eg. on arch (and adjacent) https://aur.archlinux.org/packages/proton-ge-custom-bin / https://github.com/GloriousEggroll/proton-ge-custom is pretty baller. No idea if other distros have it packaged.

The github page does have the compiled version available under releases, but as for what you'd need to do to get it to steam requires some manual work, afaik. I've only used the packaged version.

The TLDR about proton-ge-custom is that it incorporates a lot of patches, newer dxvk, etc, bells and whistles and all that. Might work better than proton experimental, might not. Worth a try?