@Edithx29_ Is the Mods folder regenerating, or at least are its contents regenerating; or is the Mods folder gone but your custom content is still present? If your deleted mods and custom content are still gone, you may be looking at the wrong Sims 4 folder, as in, not the one the game is reading. Here's how to find the correct folder:
https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/
Compare that full file path with the path to the Sims 4 folder from which you deleted mods and cc. To view that file path, right-click the folder and select Properties > General, then look for the Location.
If the mods or cc files themselves are back after you deleted them, then OneDrive may be syncing your files and, in this case, downloading any data saved to cloud storage but missing from your computer. The fix for that is to delete the files from OneDrive as well.