I believe it should be fixed now. The issue was, although the itch.io version had all the API calls removed, it was still present, which meant that it tried to stealth-launch the Steam version instead of the Itch version. Didn't flag that myself since it just works fine if you have it - which I do 😅
I've tested the latest version with someone that doesn't own the Steam version so it *should* be good now.