YouTube changed something about their API to break 3rd party apps again. youtube-dl is also broken, but they've found the issue already, so it'll likely be fixed after a while.

GrayJay and YouTube ReVanced still work in meantime.

[1] https://github.com/TeamNewPipe/NewPipe/issues/11255

I noticed this last night. Playing videos not from YouTube still works fine. This affects Piped as well.

This had happened previously a different time, which is why I tried reconstructing my music playlists with Soundcloud uploads until YouTube started working again.

I've switched to FreeTube for now, it still works using the Invidious API. This is happening because YouTube is testing forced login to watch videos or use the API. There is a workaround it seems, but we'll have to wait for all the major clients to roll it out.

This sometimes happens when youtube changes something, usually fixed after some days.

It happened on and off the past two weeks or so but was considered not a bug in an earlier report I saw. I also encountered it a few times, but since about 24 hours ago I have had no luck playing anything.

Likely changes or countermeasures on G's side, or part of the embedded as changes that is being talked about, is my guess.

I've exactly the same problem since yesterday. Didn't search for a solution, i usually just wait for next release when problems like this appears.

Yup, same here. Youtube broke something so you'll have to wait for an update. Grayjay is still working for me if you need another app to see videos.