Doesn’t iOS only use webkit based browsers? I would imagine the reason you can get ad blocking through brave is some kind of deal they have with google. Which probably means they’re just giving them all the data google would collect normally.
Firefox on iOS doesn’t have ad blocking because apple took support away in webkit. The only way brave could be doing it is by being white listed by the company serving the ad to you somehow.
Both Mac and iOS have issues with VPN usage too but that’s unrelated to webkit.