Hey, fellow dev here. How did u end up saving the data? I want to do the same for my game but not sure how.
Saving in a file that is not related to Application.persistentDataPath, because that seems to change inbetween builds on itch.
And make sure to call 'JS_FileSystem_Sync' after writing to files.
I never not-used it so I'm not sure how important is but you can look it up and see how to import it and what it's intended to do.