Curious about the reason you wish to segment the cameras, because if you just wish to block the cameras from reaching the WAN then you can create firewall rule for that, which is simply done.
Otherwise, in order to segment the cameras and the BI PC, you'd want to add a new network in the USG settings, then assign that network to the switch ports used by the cameras and PC. There would be other rules needed, then, if you also wanted, say, a smart TV, firestick, xBox, or home-located mobile device to access the BI server for the UI3.htm page or the use of the app. There would also be a change needed for the radius server for the VPN to work for away-from-home access to the app.
If you want to create a
Blue Iris VLAN in your system then please follow the steps I had outlined in the first page of this thread, and let us know if you have any questions.