if you are on android can probably download and side load the apk for a while? iPhone would be harder. There are alternatives like newpipe, and I imagine eventually someone else will create a new fork/project. there is lots of discussion on the reddit thread about what to do now https://www.reddit.com/r/Vanced/comments/tdazfr/discontinuat...

personally I just only watch YouTube on my laptop with blockers that remove all ads and using emby on mobile/tv. I never was willing to put my google creds into a non google app.