Hi,
UNtick the Dialogue Manager's Input Device Manager component > Always Auto Focus.
The Input Device Manager's keeps track of what input device you're using: Mouse, Keyboard, Joystick, etc. When you move the mouse, it switches to Mouse mode. When you use a joystick, it switches to Joystick mode. When you press a keyboard key, it switches to a mode specified on the Input Device Manager (Mouse or Keyboard). The Input Device Manager's inspector lets you specify which inputs trigger these device changes.
When Always Auto Focus is UNticked, it will only force selection onto the continue button or response menu button when in Joystick or Keyboard mode. In Mouse mode, it won't auto-select (auto-focus) any UI buttons.
Once you get that working, you may want to always allow the player to press Space to use the continue button. To do this, add a UI Button Key Trigger and set its Key to Space.