Network Switch

> I thought that a switch was supposed to [...]

   That's the idea.

> Can anyone shed any light on this?

   Based on a description as detailed as "it doesn't look like it is
doing that"?  Not I.

   Broadcast messages (DHCP requests, Wake-on-LAN, and so on) always go
everyplace.

   If I wanted to figure out what was happening in such a situation,
then I might be looking for a way to put a sniffer like, say, Wireshark,
onto a port of interest.  Failing that, I might construct a
smaller/simpler model network, where I had a better idea of all the
expected traffic, and see if it behaves differently/better.

   Otherwise, I might try asking in a more appropriate forum:

      https://community.netgear.com/t5/x/bd-p/en-home-nighthawk-pro-gaming-switches