I got back from vacay recently and can now start uploading some videos :) The camera didn't pick up a thing except for a few lights, so there's not much to see! But you can pretend, right? :)
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