I hope this video is ok. I tried layering the audio from an app on my phone, I'm unsure what i did wrong but when i saved the changes and rendered it to my phone it added about 17 minutes extra to my video, of no audio or video so i hope that this video is ok. I tried trimming the video down to when it ends but i think i missed the correct length of this video by about 4 seconds or so.
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