Hover dimensions draws the size of the group or component under the cursor. It does not edit the model, does not create a SketchUp dimension, and does not change the selection. The tooltip is: show width, depth, and height on hovered groups/components. The status line is: hover a group or component — Esc to exit.
Each number is the definition size multiplied by the scale on that axis of the transformation. A non-uniform scale makes the three numbers differ. A part that is only rotated still reports its own edge lengths, not the world-aligned box.
Move off a group or component and the drawing disappears. Switch tools, or press Esc, to leave and clear it.
A click does nothing. There is no VCB, and Tab, Ctrl, Shift, and the arrow keys are not used. There is no undo, because nothing is edited.