Nice day today so I took a bike ride. I almost pulled this video after a viewer alerted me to a typo 12 seconds into the video. Though I know how to spell, sometimes I get in a hurry. So here it is in all of its misspelled glory.
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