Hi again! Sorry about being slow at updating and the setup for the vid, this was the best I could do tonight! I've been a bit sick lately but had to record just a quick video. Got cut short in the end, hope you don't mind hehe :)
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