Did the update delete all my custom worlds? Seems like everything is gone. I made some worlds by myself with a lot of time for story and improvements and sadly uploading the worlds didn't work. So it seems like I cannot recover them. Is that a bug? Can I fix this by downgrading to the old version?
I can't speak to the other operating systems, but If you're using Windows then I believe in previous versions worlds were saved in the AppData/Roaming/Formamorph folder for the user account you're running the app from. If you're using itch sandbox, then that would be the 'itch-player' user, otherwise it would be the profile you're signed in with when playing. (The AppData folder is also hidden by default, so you'll have to enable viewing hidden items to see it.)
If the current update doesn't clear anything from that folder, then downloading an older version should work since the files should still be there.