Hello,
to disable the interface in the /etc/config/network file, the line must be present in the section of the desired interface: option disabled '1'
Example:
config interface 'mob1s1a1'
option proto 'wwan'
option modem '3-1'
option sim '1'
option pdp '1'
option auth 'none'
option metric '1'
option disabled '1'
Accordingly, in the absence of this command or in the presence of such an option disabled '0' command in the configuration, the interface will be enabled. Also keep in mind that the configuration change via the file is not applied "on the fly", but only when the router is rebooted.
The mobile communication interfaces in our routers are called mob1s1a1 and mob1s2a1. You cannot completely turn off the modem from the network file.