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.
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.