Many people have requested this, sorry it took so long. I didn't make a really long video because I'm using my phone and it just fails. Thanks for listening, commenting and subscribing! Damn I could have said subscribe haha.
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