They are in the 'Save' folder. Back it up manually or use OneDrive to keep it backed up automatically.
I think my english made you understand it backwards if I haven't made a mistake. I think I wait for the game to be complete, but thought I ask an important question here.
The thing is I thought just uninstalling a game from the itch.io PC app would make the saves and everything go away.
Still sometimes when I install a game that I thought I would never play again, suddenly the saves are still there.
That makes me think that some element keeps the saves sometimes which I don't fully understand yet. (at least on itch.io)