Anyone who primarily uses #YouTube for just listening to music (like I do) should consider trying out an app like @newpipe (NewPipe). I haven't dealt with an ad or interstitial break since I switched, and the mobile app plays sound while my phone is locked without missing a beat. I don't know if it'll be around forever, but I do know I'm never going back to just "www dot youtube dot com" for online videos again.
Edit: Android DL link for those who want to try NewPipe: https://newpipe.net/#download