What does Restore Backup do?
In the options menu of Vampire Survivors, what does the Restore Backup button do?
Backups are a feature apparently added in https://gamerunits.com/vampire-survivor-patch-notes-0-2-11-february-6-2022/ :
Backups are automatic, if you ever lose your data, it’s probably due to the game engine not shutting down completely or to a rogue file in the save folder.
Restart your machine to make sure the game is shut down completely, then launch it again, go to Options, finally click “Restore Backup” and “Confirm”
This feature is also used to
unlock a secret character: https://vampire-survivors.fandom.com/wiki/MissingN%E2%96%AF
since you need to manually edit your savefile.