So, I got my new microphone today! This video was not made with it obviously, but some people requested I do an unboxing of it when I got it. Still figuring out if I like the sound of the new mic or not. It sounds a bit muffled to me. Maybe my recorder is to blame, though.
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