Monitor mode is considered as extended function and usually, on those low-cost chip/driver, found on those boards, does not work out of the box. Perhaps some patching is needed but this is out of our mission zone - when wireless works (decently) as a station and AP mode, our job is done. In some cases, even getting here requires an insane amount of time. We are Linux for development boards, not a WiFi for Linux development boards project ... but this field is quite well supported in Armbian. We tend to include as much 3rd party USB/mPCI WiFi drivers+firmware out of the box. If you want to use monitor mode, get 8811/8812/8814 based USB adaptor. Monitor mode works out of the box on all modern kernel 4.x+