Although you said that file sharing and full disk access have been enabled, it would be better to double-check by following the steps below again.
Go to System Settings -> General -> Sharing. Ensure File Sharing is checked.
In the File Sharing section, you will see a Shared Folders list. Click the + button under the Shared Folders list and add Documents or any other folders you want.
After adding the folder, select it in the Shared Folders list. In the Users list on the right, you can set permissions for each user, or click the + button under the Users list and add another user.
Another way to troubleshoot your problem may be that to adjust folder permissions via Finder.
Open Finder and navigate to the Documents folder you want to share. Right-click it and select Get Info. In the pop-up window, scroll down to the Sharing & Permissions section. You can click the lock icon and enter your administrator password to make changes, or add another user to the list by clicking the + button and selecting the user.