Subtitles currently do not work as far as I can tell. Looks like it was recently fixed in v169, but it’s still in pre-release status (current iOS version is 166):
Nope. You have to use Android to get a decent ad-blocker.
In all seriousness; iOS REQUIRES you to use DNS level or VPN level ad-blocking typically. I think the only notable exception is that some browser apps might allow extensions. iOS still requires you use Safari browser engine though AFAIK.
Mullvad now has DoH configuration profiles with content blockers for IOS. If you actually want to select filters at a granular level, you can try Aha DNS Blitz.
I switched to Orion browser two weeks ago and it’s really good. Haven’t seen any ads on YouTube anymore, no ads on other sites either. I’ve made it my default browser. Only thing that doesn’t work for me is the consent-o-matic.