I mean if the goal is to prevent potential malicious apps from taking screenshots automatically; instead of saving a clueless user from themselves or worse getting in the way of legitimate users I believe that the proper solution is to disallow programmatic screenshots while still allowing screenshots when there is the correct button press (and ensure that this cannot be emulated). Windows reserves ctrl-alt-delete as a direct signal to the kernel for security purposes. Why can't android do the same?

> the proper solution

includes the ability from a user to take screenshots programmatically in case of need. You do not want third parties to be able to; you want the User (yourself) to be able to.