I can find the keyboard setting to select all combat units for land, air, and naval. But I can't find this hot key for selecting orbital units. I try the mod hot build. I think it is design to build units or buildings rather than selecting units. Is there a mod or some method to select all combat orbital units on the screen?
Fairly sure one of the buttons in the bottom left of the UI (below where the currently selected units appear) selects all combat orbital. It's the one with the small circle, buttons for all other unit types are down there as well. Not sure about hotkeys.