Is there a way to test Switch Control on AppleTV without a dedicated Switch device? iOS can be configure so a tap anywhere on the screen produces a switch click response, but I don't see that capability in tvOS.
There's nothing analogous to the screen switch that exists on iOS, however you shouldn't need specialized hardware to test switch control. Something as simple as a bluetooth keyboard can be paired and used for Switch Control testing. Simply pair the keyboard, and then when you go to add an external switch in Switch Control settings, press any key on the keyboard. Each keyboard key can be assigned to its own switch action.