I came across a lovely lot of jewelry today at Goodwill, so I combined a shopping haul video with a store simulation! (Sorry if there were loud noises from the necklaces clanging on the glass shelves. I'm hoping to cut down on that with practice.)
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