save file extension is the primary version of that save point. Each file number has up to six versions.You will see a long list of files with names like Slot_000000012.save or Slot_1.Find your save files at Documents > Electronic Arts > Sims 4 > Saves
If your data is corrupted or you want to revert to a previous save, The Sims 4 automatically stores numerous save points for you to choose from.