I had it downloaded via the itch.io launcher. It prompted for an update, so I updated. It gave me the error in the picture. So I uninstalled, then tried reinstalling each different version and none of them worked.
So I went into my purchase library and downloaded it directly and got the same error.
Viewing post in Sternly Worded Adventures comments
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.