I mean, technically there’s no reason a router can’t route between more than two networks. For example, I’ve got both fiber and cable Internet (for no real good reason – I ought to cancel one and save some money) and I’ve configured my OpenWRT router to have two different uplinks, reconfiguring one of the four LAN ports to WAN2 instead.

I’ve also got the other ports configured for separate VLANs (walling my untrustworthy Chinese ONVIF cameras off from being able to phone home, for example), but I think that’s technically not “routing” 'cause it’s OSI layer 2.

I assume it’s not common to have more that two networks being routed, especially in a SOHO environment, but it’s definitely not impossible.