Link to this view

Tab reaches the toolbar, then one stop each for the ports, the palette pieces and the rest of the diagram; the arrow keys move within a stop by position, Home/End to its ends.
Linking: Enter or Space on a port or piece lights the legal targets; Tab or the arrows walk the lit ones; R walks the refused ones and says why; Enter links; Esc cancels.
Inspector: focus shows it; Enter or I on a thing pins it (a click or tap does too); Esc, a second tap or Dismiss lets go.
The small buttons in a drawing (× remove a piece, ◀ ▶ move it) are their own Tab stop; Enter presses one. Enter on a thing does what a click on it does, such as firing an enabled transition in the Flat view.

Diagram