My brother sent me a long talk on YouTube and pleaded with me to listen to it. Watching was pointless the video was just talking heads sitting in chairs. However you can’t just play a video and turn off your phone while listening to the audio on headphones. The mobile browser sleeps and the audio stops. So I used yt-dlp to rip the audio and dropped it into my Plex server to listen to with Prologue. It wasn’t even about the ads, I just wanted to do some gardening and listen to something on headphones while I worked, without my phone screen on.

Firefox Mobile has an extension "Video Background Play Fix" to disable the Page Visibility API anti-feature.

on iphone, if you use youtube in the browser in stead of the app (as you should), then you can do background listening if you play the video, lock the phone, unlock the phone, play th video again, lock the phone, unlock the phone, resume play with the media controls, lock the phone.

https://newpipe.net/

You're welcome