You can use the 'Secondary key' to add a hotkey, right?

Age of Empires IV IV - Discussion
3

You can change primary and secondary keys most of the time, but there are limitations:

  • You can’t use blocked keys like ALT, Shift etc.
  • You can’t rebind some keys that involve Control+Shift

If you happen to have experience with config file editing: Advanced Users: How to rebind locked hotkeys