Followup from another angle:
I purchased a brand new original packaged but still old D-Link DWM-222. Hardware rev A1 and firmware 2.1.2EU. This device with this firmware uses a proprietary software on Windows that will configure it as I believe to be an PPP device. Theoretically a setup as PPP client should therefore be possible. I did not go that route further, as RouterOS reported “could not aquire serial port”.
D-Link provides a newer firmware 2.1.4EU and 2.1.5EU via their FTP:
https://ftp.dlink.de/dwm/dwm-222/driver_software/DWM-222_fw_reva1_215eu_win_multi_20211228.zip
These newer firmwares will change the DWM-222 to an RNDIS device compatible with RouterOS “config-less LTE” providing the lte1 interface without any further configuration. The configuration interface of the dongle resides at http://192.168.0.1/ and can be routed and reached via the MikroTik device.
Edit, another finding:
After the firmware update to 2.1.4EU or 2.1.5EU, RouterOS did not pick up the config-less LTE interface right away. In fact it was required to connect with the dongle one time using Windows. On 2.1.4EU I had to start the “StartModem.exe” in the storage area of the dongle.
Edit, another finding regarding the stability:
I noticed that the following things work/dont work:
- disconnecting the USB and replugging it while powered on - SOMETIMES crashes the connection until the MIkroTik is rebooted (no more DHCP answers from the stick, only discovers visible in logs)
- disabling lte1 and reenabling it - works fine
- doing dhcp renewals - works fine
- booting with the stick attached - works mostly fine
- storage part of the DWM-222 with an sd card inserted - works fine (in parallel with the modem function)
Edit, conclusion:
I conclude that OPs solution may be to actually push the firmware to the latest available option. The RNDIS interface is actually most likely what you want with current RouterOS versions and hardware. Correct me if wrong.