This started happening on one of my older computers recently and I had to actually disable hardware acceleration to get the audio to stop being out of sync. The tradeoff for that has been noticeable frame dropping. I even added an extension to force h264 but there's no difference.
It can play video no problem on other sites or in VLC. It's just YouTube and just on that PC...That PC can run Doom Eternal. Video content shouldn't be a problem.