For anyone still looking for a solution. I had this same problem on my Mac. When I first tried to relaunch the game after not playing in over a year there was a pop up to allow Sims access to my documents folder. I accidentally clicked deny but it never popped up again. This turned out to be the issue.
To fix it:
Go to System Preferences -> Security & Privacy -> Files & Folders -> Find “The Sims 4” in list and tick the “Documents Folder” check box to grant access.
https://www.ea.com/games/the-sims/the-sims-4/news/patch-15655
Honestly, you saved me! Same thing happened to me, I denied the pop up and my game would sometimes show me that error, so I had to create numerous folders and always copy-paste all my saves and mods, UNTIL I came across your comment! I did what you said and IT WORKED! After weeks and weeks of trying to solve this! Thank you soooo much!!!!
