Device that connects multiple networks? Layer 3 of the OSI model? Consumer ones tend to have more than that, but the more specific definition would work fine.
Yeah conceivably you could use this to ban any network device that is capable of routing between interfaces, so lots of switches with new firmware could do it, often terribly, as well as PCs with multiple interfaces. But its probably going to involve intention.
That is true, but you can also add USB Ethernet interfaces to any PC, which is even simpler.
For example, my router/firewall, which also implements various other network services, e.g. hosting my own e-mail server, is an old Intel NUC with 5 Ethernet ports, 4 of which are made with USB Ethernet interfaces.
If multiple network interfaces defines a router, then every cell phone is one, because every cell phone has a cellular and Wifi interface, and is a router in hotspot mode. Three interfaces if you count USB which can also be a network interface (hotspot works over USB in both Windows and Linux) and four if Bluetooth PAN is still a thing.
Yeah conceivably you could use this to ban any network device that is capable of routing between interfaces, so lots of switches with new firmware could do it, often terribly, as well as PCs with multiple interfaces. But its probably going to involve intention.