itch.io

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. 

It would be awesome if you could manually rearrange the order of your worlds. I have over 150 at this point, and it's a bit clunky to scroll through them. Alternatively, if there's some obvious way of doing this that I'm missing, let me know. The only method I know is exporting and reimporting worlds, which is a hassle. I'm playing the windows download.

If a world has no locations defined, then traits will not be applied. You can select them normally when entering the world, but they won't actually show up in the traits tabs or change stats.