Pretty sure it's a remote start antenna. It looks just like this one (scroll through the photos). Thank Google Lens.

 

Cool. Mind you there already is a GPS tracker built into the guardian system, unless this is one of the "chip shortage" models that were built without it. And it is connected to the also standard 5G gateway so stellantis (and potential companies that stellantis could sell this data to) has access to your location. Of course hackers could potentially access it as well.