@Froil As for your saves folder, try doing a search in File Explorer for .save files (From your C drive under "this pc") Maybe they got moved by mistake? As for your mods folder, do you use the Curseforge App? Maybe there's an option in there that accidentally deleted your mods. Do you use any other cloud services like Google Drive or Dropbox? Are they enabled for the documents folder?
One more thing: Is there any chance you made a backup sometime in the last four years? Even if it's not recent, at least it wouldn't be starting from the beginning.