Most adblocker apps can't block ads in YouTube, for reasons explained elsewhere. But, my solution on Android is the apk. "New Pipe" available from F-Droid. You'll need the F-Droid app Store first, but it's worth it if you like free, open-source software. New Pipe don't use Google Play Services or any Google API's. So, no ads, and it has background play, plus a pop-up window too. Like picture in picture. You can enque music videos to play one after another as well. I think many here would appreciate this great alternative.