This is usually against ad network rules, so if you're willing to go out of your way a bit, you can screenshot those ads and report directly to the ad network

Which is often not possible because clicking an ad generally closes the ad. And there's no incentive for users to report, by design IMO.

They could have a separate ad-reporting UI in every ad-running app (so you can report stuff later), and they could reward valid reports by skipping all ads on their network for a month or something, but doing that would reduce fraud, and that means reducing their profit. So none of them do it.

I'd say they probably need an oversight committee with teeth, to strongly punish every single violation (so the networks develop functional defenses), but they'll probably just VW-emissions-fraud their way around it.

QA is something an employee should do, not me.

Difficulty is when you don't know what ad network it is, the app hides the ad network they use, and refuse to disclose who it is.

You got served an ad from "one of our partners". That's all you'll get to know, and there's no mechanism to even report the app's shitty behavior to Google or Apple (and they don't care when the app becomes too large, either).