@valeriacoro The game will only read user files (saves, saved households and builds, custom content, etc.) that are within Documents\Electronic Arts\The Sims 4. The files on your desktop are likely intact, but the game can't find them there. But the real problem here is that OneDrive is automatically syncing the contents of Documents, which includes your Sims 4 content. So start by disabling this auto syncing:
You can still manually upload content; this is only about preventing OneDrive from uploading everything on its own. Once it's no longer syncing Documents, you can put the Sims 4 folder you moved back into Documents\Electronic Arts, and your saves and other content should appear in-game again. You'll need to remove the new Sims 4 folder that's already there first.
Before you do anything else though, it's a good idea to back up your Sims 4 folder, just in case you need it later. You can copy the folder to an external drive or USB stick, or zip it (right-click and select Send to > Compressed file) and upload it to some other free filesharing service like Google Drive or Dropbox.
