Unfortunately, there is no way of restricting folders to sections, groups nor roles in Files.

Files in Canvas does not have any form of user permissions.

The files you post in Files are available to the entire course.

If you need to share files with fellow teachers for your course, you should use nBox, OneDrive, Teams or other file sharing solutions provided by NUS.

What about usage rights and user access?

You may have come across usage rights and user access in Canvas' documentation. e.g.

Usage rights and user access refer to copyright information/status of the files/folders in Canvas.

It does not refer to permissions i.e. who in the course can access the file/folder.

There is a workaround which involves using Groups itself, since each group has its own Files. Do note that this workaround has caveats.