Or better yet, the actual adaptor type they are using. See: Adapter settings | Zigbee2MQTT
There are more than just zstack and ember:
zstack,ember,deconz,zigateorzboss
Also there is at least one user here who has had to use the depreciated ezsp adapter option. https://community.home-assistant.io/t/zigbee2mqtt-2-0-0-1-lost-connection-to-zbt-1/821471/25?u=tom_l