To hide SSID broadcast on an Asus router. This setting is available on the main wifi network but not on the guest ones.

Example, for wl0.1, the guest network 1 at 2.4 Ghz:
nvram set wl0.1_closed=1
nvram commit

2.4 Ghz Radio
wl0.1 ---> Guest Network 1
wl0.2 ---> Guest Network 2
wl0.3 ---> Guest Network 3

5 Ghz Radio
wl1.1 ---> Guest Network 1
wl1.2 ---> Guest Network 2
wl1.3 ---> Guest Network 3