The only way this will work as of now (at least in the US, I’m unsure how extensions may work on a third party App Store with the newer EU regulations) is if you use safari only. iOS allows for safari extensions from the App Store which already have things like ad blockers, but they definitely do not run within any third party apps. The code is certainly likely to be open source, but I definitely don’t see chrome/brave integrating it as part of their app bundle. Perhaps Firefox? In any case it’s up to each browser vendor to provide their own ad blocking system. For complete system wide adblocking on iOS you pretty much need a VPN.