React Native: When I add isSignedIn ternary operator statement on React.Navigator, it is saying that I sent an object as react child

I started learning React Native and doing something basic from React but it doesn't work and I can't find the problem.

This is my code, and this is the error I get.

It worked until I added the ternary statement, which should return only the screens for logged/unlogged users.

Do someone know what I did wrong or what should I do? Thank you!