Topic: Login My User Forever and Other doubts

Greeting Everyone!
Hope you guys had a wonderful day and the surroundings are safe.
Guys I'm making an awesome app that's why I need you to help me, I have used Firebase to register/login my users but I want my Users to login once only and stay logged in my app forever, But I don't know how to do. So could you please help,
The Doubts have not ended, I want the screen to switch only if the Username and Password is CORRECT, and I want to add a timer and when we time ends I want it to ring so how can I do this? One more I want to Add one coin or something as Prize after the timer rings so how can I do this? Pls Answer All the Questions.
Thanks & Regards,

Are these Firebase authenticated users, with secure rules, or just data in a Firebase project bucket?

You can make it like this logic :
When the user enters the login screen, check whether this user has been logged in?, use Block (when screen initialize) to check whether the user has logged in or not, if the user is logged in then open the home screen and if not, the user remains on the login screen

Can You pls send a video or pic of the coding?