Whenever I have issues with YouTube refusing to do things it used to do, I stop using it for a while and eventually they put it back. If you're not willing to do that, I find that the NewPipe app is better than the native YouTube app. But be warned that occasionally Google makes changes that break New Pipe and you need to wait a couple days for the devs to catch up to the change.
Yeah, I've used NewPipe for ages, but YouTube links from Lemmy open in my browser, so I'm gonna have to copy paste into it, which is going to be all kinds of annoying 😡
I tried BOW, but it didn't register Lemmy OR NewPipe as existing, so that was a dud.
I then realized that maybe I could set a global rule for all the YouTube addresses to open in NewPipe and I could so I did!
I then clicked the link that originally gave me the OP message. It opened in NewPipe.. And I got the fucking "not available in your country" message in stead!
On my phone this can be set by going to settings, default apps, opening links, wait unusually long for the list to load, scroll to NewPipe, choose the links you want it to handle.