Kxndergarten Just a thought, but are you putting back individual files or the folders they're in? If you've been using the folders, try the files instead, for example one save in the new saves folder the game creates.
Aside from that, please try playing in a new admin Windows account. Make it local, as in, not linked to your Microsoft account or any email address. Give the account a generic name with only standard characters (e.g. Test), no special characters or accents. Try to play there, first with no content, then with one of your saves, then with a freshly-download mod if the save works.