I found almost the solution in these 2 posts:
The method #2 seems the best to control directly the power of the modem.
I tried the solution with, and without, a reboot but unfortunately it does not work.
Proposed solution: echo 0 > /sys/class/leds/xxx:usbpow/brightness
“xxx:usbpow” is not present, so I try with the following one “gl-x300:green:lte”
echo 0 > /sys/class/leds/gl-x300:green:lte/brightness
Someone have an idea? why “xxx:usbpow” is not present?
Thanks,