So I installed all three MQTT modules Distributor, Transmission and Engine. I think Engine is the one I need to allow Ignition to subscribe to UMH's HiveMQ MQTT broker. My UMH installation runs on IP address

192.168.178.169

so I set the host address to

tcp://192.168.178.169:1883

in the Engine module. Unfortunately, unlike in this video, I don't see any of the tags (that I do see in MQTT Explorer):