Great! This means that your "target" device ID (for the usb-modswitch config) is 2020:2031.
You have 6 interfaces which each represents a separate function (guessing based on the umber of endpoints). The last one is a storage class, so that one is easy to figure out. Probably card reader?
The rest of the functions are all vendor specific (class ff), so they could be anything in theory. But if I am to guess, then I'd put a beer on something like:
0:QCDM
1:AT
2:AT
3:AT
4:QMI
Try adding the device to the option driver first. Install kmod-usb-serial-option and do
echo 2020 2031 >/sys/bus/usb-serial/drivers/option1/new_id
It should bind to all the 5 vendor specific interfaces, providing 5 /dev/ttyUSBx devices This doesn't imply that they work, or are serial functions at all. You still need to verify that. Use picocom or similar to test each of them. If I am correct then /dev/ttyUSB0 won't respond, although it is a serial function. It just speaks a different protocol. And if I am right about /dev/ttyUSB4 too, then that won't respond either. You should then try the qmi_wwan driver with it. To do that, you'll first have to unbind option using
echo '1-6:1.4' >/sys/bus/usb/drivers/option/unbind
and then install kmod-usb-net-qmi-wwan and add the device ID to it:
echo 2020 2031 >/sys/bus/usb/drivers/qmi_wwan/new_id
It should probe the free interface and create a wwan network device and a /dev/cdc-wdm0 device. This isn't proof of success though. You'll have to test it with uqmi to verify. Try something like
uqmi -d /dev/cdc-wdm0 --get-versions
Everything so far will only last until the next reboot, and this is obviously far too much hassle to repeat for every boot. But let us know how things go and we can add the device to those drivers by default. Then you won't have to do anything at all to make it work as soon as those changes make it back to OpenWrt