Firebase Android app with client / app authentication instead of user authentication

Question

My application does not have individual users, instead it has some data that is generated by clients, and others can see it, such as a public chat channel, usernames are also temporary.

I do not need all user account details to be authenticated. Instead, only if the request is from my application, it should be served differently. I see that there is user authentication, but that means I have to support uids tracking, etc., which also adds to the data store, another option is that I delete auth (set read / write publicly) and change data from my application.

Can I use the app’s privacy feature, which is used by the servers in my Android app, if so, how? This rule is for the server:

{
  "rules": {
    ".read": true,
    ".write": "auth.uid = 'myserver'"
  }
}

How can I make it work for my Android application?

How is my application insecure without authentication (read / write settings are public) when only I know the URL and only my package is configured from the Android application option on the server?

Is there any method other than user authentication that I can use that guarantees data security?