Edit: It seems you a many of the others replying to the GP are talking about apps from the App Store, which I basically never use. And that's sort of the parent's point, I think. I get apps from the internet, install them, and use them, like and old-school desktop/PC computer user. I rarely need to use the app store (except for updates, and it's weird UX that OS updates are in the app store to begin with) and have no compelling reason to do so.
You're right that this isn't super fine-grained. This single checkbox seems to govern several unrelated things, such as keystroke logging and insertion (Dash and Keyboard Maestro), mouse recording and control (Keyboard Maestro), and whatever APIs are used to badge Finder icons (Google and Dropbox). My belief is that an app that I haven't checked off there doesn't have access to my keystrokes. (Maybe this is wrong?) In which case I'm surprised there's nothing like this for recording the screen.
If an app has to ask me permission in order to access my keystrokes, I think it's fair to assume that the same would be true of apps that read (anything outside their window regions) from my screen. The fact that macOS doesn't require this is discoverable by sleuthing (browsing the Privacy pane, or remembering that screenshot apps don't ask for it), but there's reasonable, and probably common, mental models that don't make it obvious.
It would be like renting a house with four locks on the front door and none on the back. Yes, you could audit the house, but it's a weird asymmetry to have to look for.
(P.S. I'm older than you, FWIW :-)