How to save and load the game of the corresponding player by Serialization

Here after several days of research, I come to ask for help!

I created a menu where the player has to choose his nickname.

So that several players can play with their own backup. Unfortunately I did not find a lot of info on this problem... Aside from a little idea thanks to Aldonaletto, but since it's not by playerPrefs that I use it's a bit problematic...

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I already have my script for backup and creation of 3 users maximum... (although I would like to find a way to create more users, but I can't get them backed up in my backup file if i user fonction instatiate...)

Here's an example:

Here the username"John" was written via "InputField" and therefore a button with his name appeared.

Now I would like to from in button creates, that all the backups concern the username "John" is save.

and also for "Michael" any backups that concerns him...

I could make it work by writing three variable of each player, but that means I have to do a double job!

For example: instead of having a variable "int life = 0" for the 3 nicks I should do everything in three times.

That is to say:

"int lifePseudo1 = 0"

"Int lifePseudo2 = 0"

"Int lifePseudo3 = 0"

This is if there is a way to avoid a double job I'm curious to know the method!

Thanks in advance for your help to soon!