I think the point I was trying to make wasn't clear. My bad.
I mean that other OSes don't provide users the ability to block an app's internet permission, so NetGuard is one way people using other OSes achieve that. I mean Google might actually detect internet blocks and send data via Google Play Services to get around internet blocks. I don't know if they do do that, obviously, but I am saying it's possible.
That said, I used to use NetGuard when I had my old phone with the stock OS. I don't use it anymore since GrapheneOS's internet permission is sufficient to block apps' internet access, but NetGuard's logging and ad blocking features can be helpful too. Definitely a good app!