In the right-click menu, the wording “Use as Mask” is consistent whether you want to create a mask or remove a mask from an object. This is confusing because “Use as Mask” is the opposite of what you want to do when removing the mask from an object.
My suggestion is to update the phrasing to be reflective of the object’s current state. Maybe “Use as Mask” and “Remove Mask”. Adobe Illustrator uses “Make Clipping Mask” and “Release Clipping Mask”. Anything more explanatory would be helpful.