Darlin, you did a perfect job, despite my clumsiness (Southern accents aren't my specialty, but someone suggested it so I tried ^^; Made me really want to yawn a lot, I also stumbled over my words quite a bit so sorry!
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