It is really frustrating not being able to de-select one items with the Mac-classic “shift-click”.
When I select with the drag window and I’d like to deselect some specific item, in Mac OS I usually “shift-click” on the item, but it’s not (yet ?) working on Rhino Mac.
To expand on this, shift-click adds to the selection, cmd-click removes an item from the selection. It took me a little while to get used to this system, but I’ve since found it very useful; this way you can’t deselect something by accident.