Tapping, scratching, boxes, whispering, and other triggers. Let me know what worked for you, and I'll be sure to do it plenty more~. ((youtube decided to throw a temper tantrum on my mic quality, so sorry about that. though, to be honest, the static is almost a trigger for me as well, so maybe it'll work out for you too~~))
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