I hope you are all keeping safe and well. I think you might need headphones for this one. It's been a while and tonight I just really felt that I should get a video recorded and uploaded, despite a bad hair day and a messy bedroom. Sometimes, you just have to go with the cheap lapel mic and phone and get the job done.
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