Out of the box it can play audio in the background, and now that extensions are available you can block ads as well. You don't really need constantly updating 3rd party clients or questionable firewalls anymore if you just want usable youtube on a phone.
I'm expecting downvotes here but this is one of the reasons I started using Brave. One of the few things I could get to block YouTube ads on a non-jailbroken iPhone.
For iOS safari, I can’t recommend vinegar enough. It replaces the YouTube player with the default html 5 player. So you get all the built in iOS features and ad blocking. There’s also the sponsor block app which works in conjunction with vinegar.