Yeah…
This time I specifically went with MediaTek to have access to band selection, but MediaTek is basically all of the nails in the coffin when it comes to custom ROMs.
Other option for this would be a closed-source app like NSG with root access (meh).
Or a full-fledged Linux phone so I could just use mmcli like a normal person. That seems to exist at least on PostamrketOS: wiki.postmarketos.org/wiki/Modem (unless it’s limited in function somehow). I did test it with DWM-222 modem.

MTK Engineer Mode usually gets removed, which isn’t surprising as it includes tools like TX-test (for both WiFi and cellular modem) and someone on XDA posted a screenshot of it having IMEI change option. Both of those are likely illegal (probably not for WiFi as that’s in license-free band).