Hello,
To eliminate the bar above the title, set the screen paddings = 0.
To work with FireBase, create an object and save it in FireBase. I haven’t done an example yet, but I’m going to do it.
You write what you want to do StackNavigator as in my project. You can do this in two ways. The first way is to figure out how this is done for me. The second way is to create a copy of my project and delete all unnecessary screens, leaving only a few that may be useful to you.