I guess you either are unaware or have an outdated device. I have Brave set to the default browser on iPadOS and iOS.
There was/is previously a restriction on including dynamic content or non UIWebView/WKWebView rendering, but I'm unaware of current IAS-MAS policies.
You're also demanding the impossible/very difficult because mobile browsers don't support extensions. It's just not a thing.
Also, Firefox is already available for iOS. If it doesn't meet your requirements, then it's FOSS and you're welcome to contribute improvements that meet your requirements.
There was/is previously a restriction on including dynamic content or non UIWebView/WKWebView rendering, but I'm unaware of current IAS-MAS policies.
You're also demanding the impossible/very difficult because mobile browsers don't support extensions. It's just not a thing.
Also, Firefox is already available for iOS. If it doesn't meet your requirements, then it's FOSS and you're welcome to contribute improvements that meet your requirements.