Folders can be hidden from users who are Creators and below by utilizing the Hidden button within the folder's Options icon. First, click the Permissions & Settings button to the right of the folder.
Select the Options icon to reveal additional features. Here you can find the Hidden by Default toggle.
Clicking the Hidden by Default toggle to the active setting will hide the item from all users (as well as any new users you invite to the workspace) by changing everyone’s role to Access Denied. You can re-enable access to the folder for specific users by increasing their permissions. Click Save to hide the folder.
A hidden folder will have a transparent appearance in the list of folders.
For more details regarding adjusting a user's access to individual folders (including hidden folders) please see our support article: Managing User Permissions on Folders and Files