The official Roon advice on switches is to stick to simple switches from reputable brands. Do not go crazy complicated managed switches from Cisco – instead, go for the Netgear or TP-Link unmanaged switches. It’ll save you a ton of headaches in the long run.
this is incorrect.
No modern router has anything other than a switch built into it for the LAN ports. The ports built into the router do not act like old style hubs where they flood each port.
In fact, if any switch/router/hub is advertised as supporting 1000mbps, you can bet it’s a proper non-flooding switch, because you can’t really even achieve a full 100mbps on a flooding hub.
Some managed switches have a “port mirroring” option, but even on those you cant reliability get the full speeds of gig-e when that option is on.