For that, there's ProTube[1]. On the surface it behaves like YouTube Premium, under the hood it's just the mobile version of YouTube bundled into an iOS app. I have no idea why ads aren't served, I analyzed the network requests with Fiddler Everywhere and saw nothing nefarious.
[1] https://apps.apple.com/us/app/protube-block-ads-on-video/id6...
Holy crap I didn't know such a thing could exist, thank you. It's so responsive too.
Please delete this before anyone sees it :)
Why not use YouTube in Safari then? Haven't seen ads in years. Plenty of options to block them already.