I’ve done a bit more digging into the On/Off endpoint in the motion sensor. It appears to be an endpoint specifically related to Hue’s own software. Other Zigbee clusters associated with this endpoint are; colours, groups and scenes. None of which seem to have any impact when I try configuring them.
I think that the best thing to do in Home Assistant is to disable that entity and forget about it 
@deviantintegral Filter on device_class: occupancy to get the occupancy sensor.
I’ve created a Blueprint for using the motion sensor to control a light or group of lights here. It shows how to set the ZigBee Cluster attributes for the occupancy sensor if you are interested.