I’m guessing that you changed the video driver to GL, from SDL2? That seems to be the common culprit. Either that, or following a tutorial/script that tells you to do so.
If you’re still having trouble, open your existing Retroarch.cfg with an editor of some sorts, and look for the line that says “video driver”, and replace whatever you have there with “sdl2”. It’s in alphabetical order if that helps.
I have a suspicion that the default installation doesn’t have all the correct assets, dependencies and/or permissions set for GL to work.
If you want to fiddle, and want a more complete set of variables to tinker with, try installing it from scratch.