Programmatically show menu attached to a UIButton

I'm running into a bit of an issue with a menu attached to a UIButton in a Catalyst app. Clicking on the button works as expected: the menu appears (showsMenuAsPrimaryAction is set to true).

However, because the button is in a form as a way for the user to select from a list of available options, I also need the ability to show the dropdown menu when I tab to the button from another field. I was hoping this would happen automatically if the button could become the first responder, but that does not appear to be the case. If there a way to make this happen?