I assumed I would boot up the app and there would be a big red button saying GAMES … but no. I have to sign up to PREMIUM. Then find the YOUR PREMIUM BENEFITS section. Then find EXPERIMENTAL FEATURES and select TRY EXPERIMENTAL FEATURES. Then find the TRY GAMES ON YOUTUBE part therein and tap on TRY IT OUT.
I just use YouTube on Firefox on mobile, it does pause when you change apps but you can press play from the notification or lock screen, ublock origin also works here