It's been possible to install ad blockers for the browser on iPhones for years, without resorting to a VPN. I don't bother anymore because I'm usually at home and have a pihole anyway, but I used to use Firefox Focus—not as my browser, but to provide ad-blocking for Safari. Worked fine. Open it once to set it up (at least IIRC that was necessary—I don't remember, but there was some very-simple setup step I'm pretty sure) then never open it again. Ads blocked in Safari. Tons of other options, free and paid.

You do need a VPN (or otherwise something network-level) to block ads in apps, I think. That's a fair point.