Help-not able to adjust display brightness on external monitor after macOS beta update.

[rylinmichelle]

I have a 2020 MacBook Air M1, hooked up to an external monitor, Apple Thunderbolt Display. I updated to macOS beta 12 (21A5534d).Since the update I am unable to adjust the display brightness on the external monitor, Apple Thunderbolt Display. I have tried everything I can think of, and nothing has worked. It is defaulting at 100% brightness with no way to change it.

Is anyone else having the same issue with being unable to adjust the screen brightness on an external monitor? Is there a work around for this?

 

[ignatius345]

Since the update I am unable to adjust the display brightness on the external monitor

It kind of sounds like you have your answer. The display worked correctly (I assume) before you installed the beta and now it doesn't work. Sounds like you found a bug in the beta. It is a beta after all.

 

[RoelJuun]

It kind of sounds like you have your answer. The display worked correctly (I assume) before you installed the beta and now it doesn't work. Sounds like you found a bug in the beta. It is a beta after all.

Updated yesterday to the release version (12.0.1) and I am unable to change the brightness of my 27 inch Apple Cinema Display. Very annoying. Anyone else having this problem and found a fix?

Edit: Also the automatic brightness options are gone even though the system recognises the display. But it does change the brightness when covering the sensor, you just can't change it manually.

 

[tkpremier]

Edit: Also the automatic brightness options are gone even though the system recognises the display. But it does change the brightness when covering the sensor, you just can't change it manually.

Have the same exact problem, unfortunately no fix reported yet...i looked in System report and found that 'set brightness automatically' is set to true, but no way to disable

 

[JEKinview]

Have the same exact problem, unfortunately no fix reported yet...i looked in System report and found that 'set brightness automatically' is set to true, but no way to disable

View attachment 1904763

I, too, and having this issue: Monterey 12.1 left the Thunderbolt Display with no brightness controls. Apple agent thinks it's a glitch, sent it to engineers, and promises a callback next week. Before I continue to pour my time into free consulting for Apple, I am wondering has anyone found a solution? Thanks.

 

[MacGizmo]

I had the same problem with either Big Sur, or maybe one of the OS Betas before it. Nothing worked other than using the display controls to adjust the brightness. Unfortunately, so many displays nowadays don't have manual controls (My LG Ultrafine 5k has no physical controls). At some point, the problem was fixed with the next OS update.

 

[Artiste212]

I assume you've applied any firmware updates that exist for the monitor (or there weren't any). If so, there is a temporary workaround, if you want.

You can do what the rest of us do when we have a monitor that cannot be controlled by the Mac. There is a piece of softare called "Lunar" that uses software (controls gamma) to adjust the brightness of the external display, and will use the keyboard commands or a drop-down slider from the menu bar. When this bug has been fixed, you can stop running the software. It has given me brightness control of my two older non-Apple monitors for the first time, and it's free, so no cost to use temporarily.

BTW, there IS a setting in Lunar to control your monitor's hardware directly from the app, but I don't know if that would work with your monitor, and they have some notice that with older firmware (in general, not specific to your monitor), a problem with the monitor hardware that controls brightness could occur. So be careful about this setting.

 

[JEKinview]

I assume you've applied any firmware updates that exist for the monitor (or there weren't any). If so, there is a temporary workaround, if you want.

You can do what the rest of us do when we have a monitor that cannot be controlled by the Mac. There is a piece of softare called "Lunar" that uses software (controls gamma) to adjust the brightness of the external display, and will use the keyboard commands or a drop-down slider from the menu bar. When this bug has been fixed, you can stop running the software. It has given me brightness control of my two older non-Apple monitors for the first time, and it's free, so no cost to use temporarily.

BTW, there IS a setting in Lunar to control your monitor's hardware directly from the app, but I don't know if that would work with your monitor, and they have some notice that with older firmware (in general, not specific to your monitor), a problem with the monitor hardware that controls brightness could occur. So be careful about this setting.

Thank you for the suggestion. Lunar works for adjusting brightness on the Apple Thunderbolt. It could not adjust contrast or volume, but so be it. I had tried several similar apps that didn't work at all. In any case, since the Thunderbolt monitor is a piece of Apple hardware, and has no brightness control buttons, the company must fix their glitch. If I do hear back from them, I will post the findings here.

 

[colindgrant]

I had the same symptom but not after an OS update. I searched far and wide, and the particular startup order here fixed it for me:

Thunderbolt brightness control settings gone?

I had this exact problem. Here's how I fixed it: Unplugged the thunderbolt cord to my laptop. Unplugged the power cords of the monitors. Wait a few seconds. Plugged in the monitor power cords. Plugged in the thunderbolt connection. The brightness slider came back! I had to try it in various...

forums.macrumors.com

 

[okcsteve]

I had the same symptom but not after an OS update. I searched far and wide, and the particular startup order here fixed it for me:

Thunderbolt brightness control settings gone?

I had this exact problem. Here's how I fixed it: Unplugged the thunderbolt cord to my laptop. Unplugged the power cords of the monitors. Wait a few seconds. Plugged in the monitor power cords. Plugged in the thunderbolt connection. The brightness slider came back! I had to try it in various...

forums.macrumors.com

My system benefited from this particular startup order as well. Thank you!