LG Monitor 22MD4KA Ultrafine 4K 21.5" auto brightness?

Hi,

I have just attached an LG 22MD4KA Ultrafine 4K 21.5" monitor to the new 2019 iMac I bought.

iMac has Radeon Pro Vega 20 4GB graphics and 16GB memory and is running the latest MacOSX Mojave 10.14.6

The monitor has an ambient light sensor but it doesn't seem to be doing anything as its screen remains at whatever brightness I set from System Preferences.

I have installed LG OnScreen Control that allows me to split the screen various ways and have also installed LG Screen Manager which immediately downloaded and installed the latest monitor firmware.

However, neither of the LG apps have any info about or controls for the sensor.

System Preferences show the monitor OK but there is no option (as in the iMac's screen) to automatically adjust brightness.

The monitor user manual just says to check that the Mac software is up to date, so that's no help.

Can anyone throw some light on this (no pun intended). There are no buttons on the monitor to get into the monitor's controls like an ordinary monitor.

As it was sold as a Mac monitor I'm assuming there is some (Apple?) software somewhere that will do the job.

Thanks,

Davo