Notes:
Locked slides can still be edited by Organization Admins and Deck Admins (within presentations and the master deck). Organization Admins and Deck Admins can not be added to the Slide Restriction Editing Permissions List (as they are already able to edit locked slides).

Another important note is that a user can import the slide into a new or existing presentation, but cannot edit any of the contents on it.

Step 1: Navigate to a slide in your master deck and click the lock icon in the top right corner of the Editor.

Step 2: Enable the Editing Restriction (note this is per slide).

Step 3: You can add specific users to edit this slide. This has to be manually entered and managed.

Once the slide is locked, this is what it will show on the basic user side. There will be a red bar at the bottom of the slide.

When the user attempts to edit the slide (typing or adding components), there will be a popup as well that notifies the user. It also does not show a "save" option which is another indicator that they can't edit the slide.