They knew what they were getting into, it's never been a secret that iOS is advertising hell.

Add the AdGuard DNS configuration profile to your iDevice as a whole (no need for any separate app), and ads are blocked for everything except apps whose ads are drawn from the same source as their content.

https://adguard-dns.io/en/blog/encrypted-dns-ios-14.html

So yeah. While it won’t kill ads in apps like YouTube or Pinterest, it will kill nearly all ads in web pages and apps that source their ads from external providers.