Reading an other ticket I found a interesting way using "AT+COPS":
AT+COPS=1,2,"26203",7
It adds the "Act" (Mode). What makes me wonder, this is not compliant to the documentation for the set command but for the test command.
I also read an answer to some other ticket, which mentions, that providing the mode (AcT 7 or 9) doesn't work with COPS.
But to my very surprise, using mfw 1.3.5, it seems to work!
If send to the modem, you don't get an error.
If the modem is configured to support both, NB-IoT and LTE-M, the selector works in my tests.
AT+COPS=1,2,"26201",7
I get 26201 LTE-M (7)
AT+COPS=1,2,"26201",9
switches to 26201 NB-IoT (9)
Is that implemented in mfw 1.3.5?
If so, is that just missing in nRF9160 AT commands v2.3 ?