Hmm, I don't have a Switch but my Terraria on Xbox ought to be similar enough (they are both made by the same developer, from the same code). Summoning pets, either by activating the summon item in the hotbar, or by putting the summon item in the pet accessory slot seems to work fine. Maybe the touch-screen functionality that was added to the Switch version is interfering somehow?
Don't know anything about Duke, haven't fought him for a while.