The best way to save character progress used by 2 games?

Let’s say I split my game into 2 parts, first part gets released and after for example few months second part gets released. The problem is when I start playing second part I want to use character (with all the progress) from the first part, so I need to save the data somewhere permanently where it’s not removed even when game files are removed (cause why would you keep them if you beat the game).
What’s the best way to do it?

You might use an encoded XML file, this can be moved, bur the lpayer wont be able to change anything. Also if you save it with other things it will be more difficoult for the player to know what holds the data

As you said, it has to be saved somewhere, but not on the player computer (since he can modify it/remove it). Your only option is to create a server and sync user data directly to it. Prehaps a much simple way would be to use a FTP.