Mpv doesn't open any video files

That means you use the default configuration, so GPU-accelerated OpenGL output.

The recommended output driver is --vo=gpu, which is the default.
mpv.io

mpv has many options for video output, so using one with broader compatibility such as xv might help work around the issue.

Although this doesn’t really solve the source of the issue… Since the error comes from a mesa library, i can only suggest reinstalling the package…