@RubyHale Saves disappearing is a relatively common issue, and it doesn't always mean the files are completely gone. The Sims 4 user data folder (the one in Documents\Electronic Arts) could have been uploaded to OneDrive, where the game can't find it, in which case it would create a new one. So please check OneDrive's Documents folder for an Electronic Arts folder, with a Sims 4 folder inside. If you find it, you can put the entire Sims 4 folder back in its proper place, and Sims 4 should read your saves again.
If you don't find any saves in OneDrive, please open a File Explorer window, click This PC, and search for Slot_* (with the asterisk), which will tell your computer to search for any save files. Again, if you find them, you can put them back in Documents\Electronic Arts\The Sims 4\saves, where the game should be able to read them.