Select your save state:
This tool will fix your save state if you are encountering the issue where the game will crash when you try to save or enter any area. The crash is caused by a bug in older versions of melonDS that is triggered when the C-Gear is enabled.
Notable forks that use an old, affected version of melonDS are: Delta for iOS and its derivatives and melonDS for Switch.
After your save state has been fixed, you must immediately disable the C-Gear and avoid ever turning it on again throughout your playthrough. Remember that save states are not a replacement for in-game saves, and you must use the save feature in the game regularly as you would on a real DS, or you risk losing progress.
If you are unsure about how to obtain the save state file or how to load the fixed state, please ask the developers of the fork you are using rather than the melonDS team. We most likely can't help you with forks anyway.