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.
I’ve seen NES and combination SNES/NES clones for sale at Microcenter (or maybe it was somewhere else, I don’t recall, but it wasn’t the type of store to be selling illegal things). So, yeah. Bleem! (a commercially sold PlayStation emulator) was found to be legal in court. I don’t think hardware products doing it are any different.
The main problem is that most places selling handheld emulators out there are also bundling ROMs of every game. And that is illegal.