I just want to say thank to everyone who's help me get to the point of where I'm at, I'm so appreciate of it. You silly's really mean so much to me and I can't thank you enough.
To listen while using other apps, switch the player to Picture-in-Picture (PiP) during playback — it keeps playing in a small floating window (the screen stays on).
To listen with the screen fully off, in-browser playback stops by YouTube's design. Open the video in the YouTube app to keep listening where background playback is supported (e.g. with YouTube Premium).
Open in YouTube app