Disable 2.4Ghz

Scratch the idea that 2.4GHz or 5GHz or Guest_24G anf Guest_5G  are network.

Essentially you have a kind of two networks:

The primary, normal one with the LAN ports plus wireless devices associated to the router network by the "normal" SSID(s).

The second, intended for guest usage, where wireless guests (or for the sake wireless IoJ) devices can associate to the guest network. By default, these devices can't see each other, and each device can connect to the Internet only. There is an optional control for the guest network(s?) where you can enable "Allow Guests to see each other and access my local network". This is not what you want of course, so the only choice is operating the guest network without this additional allowance. This does lead to the situation that each device on the guest network can only access the Internet, the IoJ cloud only. Making it little bit difficult if the IoJ need to communicate - especially if it's for home automation and the Internet is down.

To be technically exact, these devices have only one network, one LAN, one IP subnet. The guest network MAC addresses are just L2 filtered, so (by default) these guest devices can reach only the Internet, but not the other devices on the WLAN and the LAN ports. Be aware for testing that the devices on the "two" networks can ping each other, also the DHCP service is the very same. Any other services are not reachable

There is no reason to operate the IoJ guest network only on one wireless radio. There is no added security. You are only crippling the wireless availability and coverage for your "normal" devices. Said that: For these reasons, there is no such software control available.