Cannot change brightness with displayport of Alienware monitor

[amsocial]

Hello
Just got my AW3821DW monitor.

I am using a mac book pro 2018.
When connected with the display cable I cannot adjust brightness and the ambient sensor is off and get refresh rate 60.

With HDMI cable both are working but refresh rate is 30.

I have tried with 3 display cables.

 

[svenmany]

I drive an old Apple display with DisplayPort from my MacBook Pro. I have to also connect USB to allow my MacBook to adjust the brightness. Could that be the issue? Admittedly, I have very old tech.

 

[amsocial]

Thanks svenmany. You use usb dongle to connect to connect to display port?

One thing I noticed is in safe mode I can change the brightness

 

[svenmany]

Since it works in safe mode, you might have a different issue than I had.

Just so you have my complete picture:

I'm connecting a 2018 MacBook Pro to a 17" Apple display. The display was bought in 2014, but the manual I just downloaded for it was printed in 2010. So, it's an old monitor.

I have two thunderbolt ports on my 2018 MacBook Pro . One has a USB-C to DisplayPort dongle that connects to the Mini DisplayPort of the monitor. The other has a USB-C to USB-A dongle that connects to the USB hub of the monitor.

Each dongle uses a different aspect of the thunderbolt port they are plugged in to. One just takes the display information. The other just takes the USB traffic. My understanding of Thunderbolt is probably naive.

If I don't connect the USB hub of the monitor to my laptop, I cannot control the monitor's brightness from the computer.

Good luck sorting it out. You seem to have bought an amazing monitor.

 

[amsocial]

Thanks, monitor is awesome

I am going reinstall OS, to rule out 3rd party app messing with ports.

 

[amsocial]

For anyone who stumbles on this, the issue was HDR. Needed to turn off HDR to get brightness working.