RedBaronnes This error is somewhat misleading in that game data isn't typically missing and may not be damaged. You've already established that the problem is something in the Sims 4 folder you've moved, so it shouldn't be too difficult to find the culprit.
Start by testing your mods and custom content in the new Sims 4 folder the game has created. Don't reuse your old Mods folder or its Resource.cfg file. Instead, move individual mod and cc files to the new folder and see what happens. If you have a lot of them to go through, the 50/50 method can make the process much more efficient:
https://modthesims.info/wiki.php?title=Game_Help:Finding_Problem_Custom_Content#The_50.25_Method
Once you've done that, copy over the contents of saves, then Tray (saved households and builds), plus Screenshots and Recorded Videos if you care about those. The other files and folders can be discarded.
