Step 1 - be hot. Step 2 - sweat profusely from every pore. Step 3 - feel your insides liquify and turn into tomato soup. Step 4 - make a grilled cheese. Step 5 - eat said grilled cheese and throw away your tomato soup because it is inferior to tomato bisque and literally any other soup.
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