That means something in your opengl driver/hardware seriously screwed up. Maybe the zero-copy path will fare better but not too likely. You should also try the standalone MPV to see if it is different (you should be sure to check the app’s logs and apply the same MPV options or it won’t be a proper test).
Started investigating the zero-copy path issue, and specifically EGL. I was using the proprietary nvidia drivers as provided by Debian 11 (bullseye), as the nouveau drivers were causing issues. Decided to download directly from nvidia, and after installation, voila… this issue disappeared.