Which phone do i need to purchase in order to be in control of it? (i.e. some apps are blocking my ability to take screenshots ... wtf?) I know there are different communities working on liberating phones, but have not kept myself up to date, what is out there? what can you recomend?

You can checkout the Google pixel phones and put GrafeneOS on it. It gives control over almost everything. I am running it on a pixel 6a and can tweak everything I wantYou can checkout the Google pixel phones and put GrafeneOS on it. It gives control over almost everything. I am running it on a pixel 6a and can tweak everything I want

Can you do split-screen, set the other app active, then screenshot from that and maybe capture the whole thing?

A custom rom should give you the freedom but you'll likely end up with something more trouble than it's worth. An app that blocks screenshots (eg: banking apps) will likely also block custom roms and unlocked bootloaders. Workarounds exist, but it's a constant cat and mouse game.

Not the answer you are looking for I guess, but iPhones does not allow apps to block your ability to take screenshots.