Installing Powerslide again on my Win 10 System and Nvidia RTX . The game is going well so far, only the textures of the surroundings look terrible. Just rough blocks everywhere. I've tried all of the settings, resolutions, and compatibility settings.
Does anyone have any advice, a patch, a solution? Thank you.

Try dgVoodoo 2.

http://dege.freeweb.hu/dgVoodoo2/dgVoodoo2/

I've tried installing the latest dgVoodoo 2 files into the Powerslide folder, but it made no difference other than the option of a broken Banshee driver over software in the graphics settings. Is there a particular dgVoodoo 2 version I need to setup and what settings are required to fix the textures?

Try a different output API in the dgVoodoo 2 app (which normally says best available one), go from the highest DX version to the lowest until you have one that works.
If that doesn't help, in the DirectX tab of the dgVoodoo 2 app you can choose several legacy videocards, maybe one of them solves the problem.

Or just contact gog support.

After setting the game to run as administrator, I somehow got the Banshee drivers working and it resolved the problem with the textures. But thanks anyway!