Hi @ Riquelme Silveira,
Thank you for posting in this community.
We can accomplish your needs by setting read permissions for folders and giving edit permissions to files in folders.
1.Select the folder, right click your mouse and check Manage Access.
2.Click on Advanced Settings at the top.
3.Click the Stop Inheriting Permissions button.
4.Assign read permissions to your users or groups.
5.Perform the same operation on the file, except set the user's permissions on the file to Edit(or above).
You can see that the folder is marked with no editing and that moving or copying the folder is prohibited.
In fact, there is no out-of-the-box way to disable user modifications to the folder structure in SharePoint. We can only restrict users from modifying folders by setting folder permissions to read (which means that folder name changes are not possible) to restrict moving or copying folders.
This can be a complicated operation as we need to break permissions for each folder and file.
Also, there is a limit to how many SharePoint folders can break permissions:
If, however, you have a large number of files, then I am afraid the method I have provided won't work. We don't have a better solution to this problem.
Thank you for your kind understanding.
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