It seems YT started another attempt at blocking alternative clients. They changed something in their API and both SmartTube and Tubular (NewPipe fork) are completely broken. Apparently it started happening this past week, but we personally just felt it today.
Edit: SmartTube already has an update but still not working for 4K videos it seems. Tubular still not working but it might be due to the upstream (NewPipe) is still working on a fix.
I should point out that this isn’t always “Google is trying to block adblockers” again!
Google can, will, and does simply change how the YouTube watch pages look, feel and operate behind the scenes quite regularly.
Thankfully we have people like those at the FreeTube, NewPipe and yt-dlp projects to sift through those changes and update the code to cope with the new output.
Yeah! Freetube already has a patch committed, which is impressively fast.