PPP mode appears to be 0 ECM (ethernet/CDC) appears to be 1

Despite changing it to PPP mode I think you need to change the USB identifier as well?

To get it to work with Opnsense I ran the following commands and then power cycled it.

AT+QCFG="usbnet",0
AT+QCFG="usbid",11388,293

This sets it to PPP mode and changes the USB identifier to match EC25 in PPP mode.

Easiest done in Windows with QNavigator and the correct drivers Quectel_USB_Drivers_For_UC20&UC15&EC20_V1.1.

Wine on Linux

It may be easier to just use minicom/screen to connect to the ttyUSB2 port 115200 baud but it didn't seem to work for me when I first tried it. A second attempt and I could send AT but it didn't echo when typing and just showed OK...

Not recommended, when changing to ethernet mode (cdc) the serial ports disappear from linux and you cant reconfigure it.

Using QNavigator in Wine32, with WineTricks enabled:

dpkg --add-architecture i386
apt install wine32 wine64 winetricks
WINEARCH=win32 WINEPREFIX=~/.win32 winecfg
WINEPREFIX=~/.wine32 winetricks mfc42

[ 1549.047609] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB0
[ 1549.051576] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB1
[ 1549.058275] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB3
[ 1549.059522] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB4

symlinked com ports into wine:

lrwxrwxrwx 1 root root 12 Nov 25 03:08 /root/.wine32/dosdevices/com33 -> /dev/ttyUSB0
lrwxrwxrwx 1 root root 12 Nov 25 03:08 /root/.wine32/dosdevices/com34 -> /dev/ttyUSB1
lrwxrwxrwx 1 root root 12 Nov 25 03:08 /root/.wine32/dosdevices/com35 -> /dev/ttyUSB2
lrwxrwxrwx 1 root root 12 Nov 25 03:08 /root/.wine32/dosdevices/com36 -> /dev/ttyUSB3
lrwxrwxrwx 1 root root 12 Nov 25 03:03 /root/.wine32/dosdevices/com37 -> /dev/ttyUSB4

WINEPREFIX=~/.wine32 wine Qnavigator.exe

Connected on com35 -> ttyUSB2.

Ran commands:

AT+QCFG="usbnet",1
AT+CFUN=1,1