Set plot, graphic object or layer to be unselectable to prevent selecting it in graph and editing it with mini toolbar, regular toolbars, etc.

Clicking the item in Object Manager is always supported. The Mini toolbar button can be used to turn selectability back on.

Corresponding LabTalk property for graphic objects object.mouse=0 not selectable or 1 selectable

For layers in graphs, selectability can also be globally (it is an Origin setting) prohibited by setting @GRLS=0.