The save system is still broken, unfortunately.
Viewing post in AntNest Metroidvania Map Maker comments
I'm using the offline/browser version. The problem is specifically that there's no option to save, as the Download Map button is nonexistent, and in both the itch launcher and the normal website the hotkeys don't work
Specifically the issue is that there is no option to save your progress, either you save the full image, or, it just deletes all your progress.