This is a very broad idea where an old game cartridge is retrofitted with some form of new gadget. For this example, a mini PC was fitted in between a Nintendo 64 cartridge. Because cartridges can be disassembled into two halves, just about anything could be wedged in between.
Game cartridges could be turned into a plethora of devices: mini or single board PCs, game consoles, streaming boxes, NAS servers, Bluetooth speakers, smart assistants, and so on. Even small Game Boy cartridges could be turned into USB wall adapters.
And yes, it would be preferable if dead games (or common sports games) are used, but if none are available you can buy blank cartridge shells just about anywhere.