Is game console (hardware) piracy a thing?

The correct term is: bootleg, in this case. As in for example: the real Switch 2 is expensive, so bootleg imitations (knock offs) exist sold for cheap. You can encounter that in a literal market where they are selling fake iPhones, watches, handbags & etc.

You could 3D print a game console but it’ll be obvious as it won’t work without internal components (GPU / CPU), you need to obtain a schematic of its design in order to really create a copy. An iPhone is made from aluminum for example.