[2020] HELP! Game crashed during save, simulation failed

If the Loading Screen Mod's recovery + Save Our Saves isn't doing it, you can try also adding Safenets and doing all 3 at the same time. I doubt that will help though. It sounds like the power got cut of before it was done saving, so the file may just be corrupted. Do you have any other versions of the city? An older save or an autosave?