You cannot disable this completely on an MX, unfortunately.  We seem to have found a workaround, though:   Minimize the power of the 2.4 GHz band to make it virtually invisible by setting it to 1 dbm.   Go to Security & SD WAN -> Wireless Settings Scroll all the way to the bottom of the page Change the Transmit Power for the 2.4 GHz band to 1 dbm Click Save Changes Of course, don't do this if you have any devices that cannot use 5 GHz, because those devices will no longer be able to connect. ... View more