Can't control monitor volume with keyboard on 2018 Mac mini [duplicate]

I just decommissioned my 2011 iMac and replaced it with a 2018 Mac mini and a new 27" monitor. The iMac is where I used to play audio and controlling from the keyboard (F10 - F12) was never a problem. I am now connecting to the new monitor via HDMI (v1.4). It will play audio, but I can't control it from the keyboard - I get this instead:

When I go to the Sound in System Preferences, this is what I see for output:

This leads me to believe that connecting via display port might possibly give me the ability to control via keyboard? I can't seem to get a USB-C to mDP cable to send a signal, so I'm guessing I need Thunderbolt 3 to mDP. Does anyone know if that will work before go and buy the cable?

Any other tips that may work for getting control of the audio on the keyboard when connected via HDMI v1.4?

Solution 1:

I basically had the same issue when connecting my ViewSonic VA2265 monitor to my 2018 Mac mini using a HDMI cable. When selecting the VA2265 from the Sound pane of System Preferences, the volume was set to maximum and could not be adjusted. I can adjust the volume by using the controls on the monitor, but this was not desirable. Below is a screen shot.

The solution I used was to plug a stereo cable between the monitor and the Mac mini External Headphones jack. I then configured the monitor to select this jack for sound input. Below is a screen shot.

The volume can now be controlled from the keyboard.