obnizOS will search for stored settings so that it can connect whether it is a stealth SSID or not. Therefore, there is no special setting for stealth SSID.
Notes on the channels used
You can use the stealth SSID for channels 1-11, which are available internationally, but you cannot connect to the stealth SSID for channels 12-14, which are available in Japan, because obnizOS does not perform an active scan. Change Wi-Fi Region from setting (OS3.5.0 or later)