There are many reports of live lyrics rolling out to YouTube Music for Android (version 6.15) and iOS (6.16) today. You might want to Force stop YTM from App info before checking, and be sure to try multiple songs if you don’t see it immediately.
This rollout is not tied to the updated Now Playing UI that adds comments that’s also being tested.
No they’re definitely different. Just pick a video that’s not just the song