Back to not using YouTube on mobile.
Firefox + uBlock Origin + Video Background Play Fix
uBlock Origin -> removes the ads (but no sponsorblock) Video Background Play Fix -> lets you turn off the screen or switch tabs with it still playing
The F-Droid guys have forked Firefox for Android to let you use any extension you want. They named it Fennec as the older Firefox, but is just the name, the codebase is the new Fenix one.
Doing none of that and just pay for YouTube premium.
Why?
Because sponsorblock is fantastic and I can set my default video speed to 2x.
That's it. That's all I wanted. But I was more than happy to install and maintain the app to do so.