For adblocking, You can get Content blockers from the app store that you enable in the settings, Personally I use Adguard Pro.
I've also got an Extension that makes websites Dark mode called 'Noir', You can adjust settings global/per site if they dont look good.
Extensions/Content blockers are limited to Safari (to my knowledge).
Just scroll down to method 2 and download the profile from the iOS section. You’ll need to be using Safari for the download to work properly. Then if you ever need to disable it the setting is in Settings > General > VPN & Device Management
If you use the app then you have to pay for their subscription to use DNS features. If you don’t pay then you’re really just limited to adblocking in Safari. The profile I linked is free and will work for all apps. It’s not as robust or customizable as the AdGuard app, sure, but I’ve never had any real issues or need for anything more. Plus it’s one less app to have installed.
It actually is a detriment because the app also download and apply quite a few filter lists that can block annoyances like website cookie policies, and way more ad categories that a simple DNS filter cannot address, and other shit like Javascript bitcoin miners