Copy the Sims 4 folder in the local version of Documents\Electronic Arts to your desktop, then disable OneDrive's auto syncing of Documents. If you get a message about a folder being in use, it's probably because OneDrive is syncing in real time.
If you're having trouble finding the Mods folder on your hard drive, open a File Explorer window, click This PC, then C, then Users\\Documents\Electronic Arts\The Sims 4. You know how to get into OneDrive's Documents folder already. The simplest, if it works, is just to delete the files on your hard drive and then in OneDrive immediately after, so no syncing happens.
