Hello there,

Unfortunately, we weren't able to test the game with Windows 10 much at all, but as you said, it doesn't sound like this is the non-latin letters problem some other players have had - though you can test that too by running the game on a guest account if you want to make sure. Using the Microsoft login shouldn't make a difference at all - it's all about the 'username' part in the saving folder that has to be latin characters only. (C:\Users\USERNAME\AppData\Roaming\Shark Punch\The Masterplan)

Another common issue with saving games are the Windows permissions, as well as firewall and anti-virus software that all may prevent the program to write/make changes to files - meaning it also cannot edit the save file, i.e. to save the game. To counter this, make sure The Masterplan.exe is added to your protective program's 'allowed' or whitelists, and run the game as admin, preferably on an admin account.

Hopefully you'll find one of the above helps out - please let us know if you find a solution to this!