Come give me a language or accent and I will attempt to do my best at it. You can tell me what to say in any language and I'll google translate it and you can watch me fail at it haha :P
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