The BR2 pro is dual 5G. Look at all the antennas!!
It has 8 cellular antenna connections (1 x GPS and 2 x WIFI) - so the physical size to support that number of connections (and then heat dissipation of dual 5G modules) is the biggest reason you’ll not see a dual 5G transit.
Your transit Duo is a great device. Just plug a 5G router in its WAN port and then bond dual LTE and teh 5G connection.