In the Default Keyboard Controls, Comms section (Filtered by ALL) two typos exist which can be confusing. Two of the COM3 titles and descriptions in the sidebar refer to COM2 when they are in fact for COM3.
They are “Set COM2” and “Set COM 2 Standby”. Notice also that the latter has a space between COM and the number, which isn’t the case for COM1.
Look in the controls for COM3 and you will see them.