I just updated today and it's doing the same thing for me. I tried different versions and several are broken, plus it's asking me to buy the game again for some reason.
An easy way to handle this that doesn't require waiting for me to get the fix out or edit save files, is to load the Steam demo, then quit and go back to the itch version.
It's a script that affects migrating old save data, that had a last minute addition specifically for the Steam version that shouldn't have been enabled for the Itch version.