Was getting "OPENGL ERROR: failed to choose pixel format for dc" in a dialog. Proton log was shoing "err:wgl:X11DRV_WineGL_InitOpenglInfo couldn't initialize OpenGL, expect problems".

... I had tried different Proton versions including GE but the ultimate fix was to clear out all the tweaks and install the lib32-nvidia-utils package from Official Repositories (multilib).