I've seen the effects on invidious these past days. 8 in 10 instances have been broken. Google is putting some serious work into shutting alternate frontends down. Shows you how much of a dent they're putting in the bottom line.
Invidious and YouTube piped (and LibreTube) by default load the videos server-side, as opposed to GrayJay, NewPipe or Smarttube.
It has advantages (mostly that your IP address is not shared with YouTube, and it allows users from countries where YouTube is blocked to still access it) and inconvenients (much harder to keep up when YouTube actively seeks to block them).
Fair enough, that's interesting. I assume this only applies to the non-web clients. On the web, it would not be possible.
You can verify by looking at the outgoing network requests on this random video for example: https://invidious.privacyredirect.com/watch?v=qKMcKQCQxxI
Because of the CORS settings on Google's servers would tell your browser to not go forward with the request.
There are two ways it could eventually be possible:
By opening the video in a new page/tab that only contains the video, with the YouTube player, which defeats the purpose a bit.
I remember Hooktube. That was when front ends were still trying to play nice by accessing youtube the "right way".
They killed that one off pretty hastily.
Invidious was the hero successor, but I think we all knew that it would eventually come to this. Invidious' most recent fixes for blocking involve passing identity tokens, making a concession that Google is then better able to track users behind Invidious.
I'm not sure how much farther there is left to go on the technical angle of this fight.