Super specific question may only be best answered on a Ram forum (i.e. is there a factory harness to HDMI adapter?) My experience in this area is tangentially related (my car had a junky UConnect 3) but I would expect the answer to be unlikely and not with software alone. I have seen some adapters that allow multiple RCA inputs into a factory head unit, particularly if it already has one (your’s is a 2018 so I believe it’s legally required to have a backup camera.) Then you’d have to consider, where is your map/ham app coming from? The Pi? A phone? You may need additional hardware/software to achieve.
All considered, I ended up replacing my unit because I wanted CarPlay and HDMI came along for the ride. Once I started messing with Pi in the car you realize there are some drawbacks to head unit for this application. It counts as a “source” so your music stops while viewing HDMI… Less than ideal.
There are some decent affordable brand name units out there, most of which support HDMI. If you can I would try them out and see if they suit your needs. Otherwise a secondary display would be easier and cheaper, but likely DIY looking. Sounds like you were looking to have a clean OEM look.