rellhom this is wrong of Android and iOS to even allow such system level abilities by apps
That is a valid opinion. But what comes next?
Empirically it seems as if some app authors want the ability to block screenshotting and/or screen recording. I doubt that Apple or Google decided all on their own to add this ability.
So if app authors want such a restriction and can disable their apps on platforms that don't enforce those restrictions, and if users want to use those apps, what comes next?
One option might be for GrapheneOS to maintain the screenshotting and screen-recording restrictions that app authors want, so that app users can use those apps, while some other organization tracks GrapheneOS builds and issues an OS which is exactly like GrapheneOS except that it allows arbitrary screenshotting and screen recording. Perhaps the GrapheneOS project would be successful at getting banks, Netflix, etc., to trust the platform even outside of Play Integrity, and users willing to live with those restrictions would be able to use those apps. Users unwilling to live with those restrictions could then use the GrapheneOS-tracking OS instead.
Another option might be for GrapheneOS to ignore screenshotting and screen-recording restrictions. Presumably that would make it harder for banks, Netflix, etc., to trust the platform. Then maybe all GrapheneOS users would be unable to use those apps.
I'm not saying I know what "the right answer" is. But it's also not clear that deploying one reasonable principle (such as "It's my device so I should be able to do whatever I want with it") without balancing it against other issues is always the most productive approach.