Unity game security, how to implement correctly?

Question

Burglary protection

How is security in multiplayer mobile games?
How to properly store player data in the database?
How to make detection of new and former players without registration/login tab? (For new players to register in the database and players who used the game to restore their data in one click) only Google Play Services comes to mind.
Is it possible to register through Google Play Services and write data, for example, to MySql?

At the moment, my game can simply be decompiled, a part of the script can be changed, and any button can be used to issue the game currency.

Answer 1

At the moment, my game can simply be decompiled, a part of the script can be changed, and any button can be used to issue the game currency.

the problem here is that you implemented the game logic of the network game on the client side, instead of doing it on the server side.