I am slowly trying to build up to having a tiny cluster Raspberry Pi 4s at home. I have 2 of them (so far) connected to a small switch. I needed internet connectivity and I use this little tiny pfsense box at home https://www.netgate.com/solutions/pfsense/sg-1100.html
It is lovely and works wonderfully.
Just due to where everything is located I did not have any open ports physically near where I was at so I wanted to use the OPT port on the Netgear. Almost all things network are somewhat challenging and there are tons of misinformation on how to use the OPT port on the web.
I ended up using this guide.
In short, you have to enable the OPT interface and do not assign it an IP.
Then create a bridge between LAN and OPT.
Then finally add a firewall rule on LAN but select the OPT interface. The rule I added there was basically allow everything just to verify things were working.
Once that is done plugin and use ping to verify it works.
One thing to note the IP address you get on the OPT port come from the DHCP so you are not on a separate LAN. In my case that is what I wanted.