The "garage door" setting will set open/close state based on the "xyz" coordinates of the device, so it will report "open" when the door is raised because the sensor is oriented one way, and "closed" when the door is down because the sensor is oriented in the other direction. For this, you do not need the magnet piece, which is how open/close works otherwise. As the name suggests, this won't make much sense unless you're using this on a garage or other overhead door.
The second setting controls whether "xyz" (three-axis) reporting happens at all. It's likely not available when in garage door mode because those values are used for a different purpose, but the option is presumably here at all because if you don't actually want to detect position changes, disabling this will cut down on reporting from the device and, in turn, events on Hubitat. If yours were enabled, you'd see a "threeAxis" attribute under "Current States" in your screenshots with X, Y, and Z coordinate values.
