So those two navigation graphs can be completely separate navgraphs, after login you go to the root of the right graph and from that point on it doesn’t really matter that the other one exists, you make those screens only let you navigate to the right destinations.
Bonus points of those are not in the same module so that navigating to a “nasa” destination from an “admin” destination would just be impossible to do by accident if you can’t reference those destinations in the first place
Would smth like that work for you here?