All video players were failing to load videos (with "Unknown" error in the logs) for the past week for me. It doesn't matter which video or from which website, they all failed. Today, I tried switching to Proton 10.0-4 and it fixed the issue (but it logged me out, reset all of my settings and cleaned my recent avatars list). Then I switched back to Proton Experimental... and the video player issue happened again...