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Safari. With 1Blocker and SponsorBlock.

„But what about listening in the background?“
Simple.
Video in Full-Screen, put Safari in background and activate videoplay from the Control Center.

I don‘t need a YouTube app. It just forces me to sign up and watch ads.

Good point. Guess most apps are kinda like that. Except paid ones maybe.
 
Safari. With 1Blocker and SponsorBlock.

„But what about listening in the background?“
Simple.
Video in Full-Screen, put Safari in background and activate videoplay from the Control Center.

I don‘t need a YouTube app. It just forces me to sign up and watch ads.
Just use pipfier
It’s free and take a second
 
There are quite a few in the App Store with background audio, no ads, PiP and such if you want video.
I still use Video Lite as I bought for 9.99 euro once years ago and still works great, however it is for quite a while subscription only (cheaper then YT though). Other great options are:

- SmartTube (free)
- SwizzTube

There are also some great dedicated audio ones:

- MeMusic
- Youtify
- Apollo Music
 
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