There is a custom page that I created and shared with all the teams here. It has the 'custom list' app in it. The weird thing is they are not able to add/remove columns to the page. The button is greyed out.
This is working as designed. Only the administrator that created the the shared page with the custom list is allowed to add or subtract columns.
As another option for a user who wants to configure their columns differently, the user can copy that shared page to the menu on which it is located.
To do this:
1. Go to the shared page
2. Click the gear icon at top-right
3. Click Copy Page
The new page will be created. As the owner of the copied page, the user can then add or remove columns as they wish, regardless of their permissions (viewer/editor).