Polymega's N64 module allows users to install Game Boy and Game Boy Color games to their system, thanks to the N64's Transfer Pak.
The Transfer Pak was originally intended to allow connectivity between N64 and Game Boy software, but, when connected to a controller on the Polymega, it allows you to dump the game ROM to the system's internal storage.
Sadly, that's as much as you can do at present – but it has been revealed on the Polymega Discord that a Game Boy and Game Boy Color emulator is in the works for Polymega, and you'll be able to play these games on the system.
According to one of the team working on the system, Game Boy support hasn't been added yet as Playmaji wants to make sure N64 support is as good as possible for the time being. A "MUCH bigger" system update is on the way "that has ALL of the stuff that we wanted to do", which includes adding the company's 'Cerberus' Game Boy emulator.