Built-in XDR display brightness repeatedly forced to 100% while BetterDisplay is running

[fylucion]

Issue

The brightness of my MacBook Pro's built-in Liquid Retina XDR display
suddenly became stuck at 100% while BetterDisplay was running.

Whenever I manually lowered the brightness, it immediately jumped back
to 100%.

Investigation

While the issue was occurring, I monitored the following macOS log:

/usr/bin/log stream --predicate 'eventMessage CONTAINS "DisplayBrightnessSystemBannerContent"' --style compact

I found that brightness assertions with a value of 1.0 were being
generated continuously at approximately 12 Hz, or about 720 times
per minute.

Example:

Did activate assertion for DisplayBrightnessSystemBannerContent(value: 1.0, range: 0.0...1.0)

BetterDisplay A/B test

I then quit BetterDisplay:

osascript -e 'quit app "BetterDisplay"'

Immediately after BetterDisplay exited:

• The repeated brightness assertions stopped.
• A 10-second observation window showed 0 repeated events.
• The built-in display brightness became controllable again.

The observed behavior stopped after BetterDisplay was quit, suggesting
that BetterDisplay may be involved in the repeated brightness changes.

Trigger

The exact trigger is currently unknown.

BetterDisplay had been running normally for approximately 4 days and
13 hours before the problem suddenly started.

Therefore, this does not appear to happen immediately after launching
BetterDisplay, and I have not yet been able to reproduce the trigger
intentionally.

Display setup

• MacBook Pro with built-in Liquid Retina XDR display
• External Samsung display also managed by BetterDisplay

The external Samsung display did not exhibit the same 100% brightness
behavior.

Additional information

I checked BetterDisplay's configuration after the issue occurred.

The built-in display showed a hardware brightness value of 1.0,
while the external display retained normal lower brightness values.

However, the configuration file was modified after the brightness loop
had already started, so I believe the 1.0 value was a consequence of
the issue rather than the original trigger.

Please let me know if BetterDisplay diagnostic logs, configuration
files, macOS logs, or any additional testing would be useful.

[waydabber]

Can you please extend this with detailed configuration description and all versions (macOS, BetterDisplay etc) involved? Also, please give some additional details like Apple Preset used, is brightness upscaling in effect (direct or software?), etc. These details may make the issue report a bit more actionable. Thank you!

[fylucion]

Thanks for the reply. Here are the additional configuration details.

System

• Mac: MacBook Pro
• Model Identifier: Mac17,2
• Apple Silicon: Apple M5
• Architecture: arm64
• Memory: 32 GB
• macOS: 27.0
• macOS build: 26A5388g

BetterDisplay

• BetterDisplay version: 4.3.5
• Build: 50105
• App location: /Applications/BetterDisplay.app

Built-in display

• Display: Color LCD
• Type: Built-in Liquid Retina XDR Display
• Native resolution: 3024 × 1964
• Refresh rate: ProMotion
• Apple Display Preset: Apple XDR Display (P3-1600 nits)
• Automatically Adjust Brightness: Enabled
• True Tone: Enabled
• Mirror: Off
• The built-in display is being used as an extended display.

External display

I also have one external display connected:

• Display: LS27F61x
• Resolution: 3840 × 2160
• Refresh rate: 100 Hz
• Main display: Yes
• Mirror: Off

So the setup is one MacBook built-in XDR display plus one external LS27F61x display, with the external display configured as the main display.

Brightness upscaling

Brightness upscaling is not in effect.

In the BetterDisplay UI:

• "Brightness Upscaling" is not enabled and is unavailable in my setup.
• "Allow direct control and XDR upscaling" is disabled.

The BetterDisplay preferences also contain:

• autoActivateNativeXDRUpscaling@Display:2 = false

For completeness, the preferences currently contain these brightness-related values for the built-in display:

• hardwareBrightness-AppleController = 0.4225000143051147
• softwareBrightness-ColorController = 1
• combinedBrightness-CombinedController = 0.5625

I am including these only as potentially useful diagnostic information. I do not assume that the softwareBrightness value means software brightness upscaling was active; the BetterDisplay UI shows brightness upscaling as not enabled.

Behavior / reproduction

The issue affects the MacBook's built-in XDR display.

While BetterDisplay was running, I observed the built-in display brightness being pushed to 100%.

In one observed case, BetterDisplay had not been responding to CLI brightness commands, and the application was then explicitly opened with:

open -a /Applications/BetterDisplay.app

After BetterDisplay was opened, the built-in display brightness jumped to 100%.

The CLI command immediately before this was intended only to control the external LS27F61x display, not the built-in display:

BetterDisplay set -nameLike=LS27F61x -brightness=0.5

The external display was successfully set to 50%, but opening BetterDisplay itself coincided with the built-in display brightness jumping to 100%.

I have since stopped using BetterDisplay for brightness control because of this behavior.

Please let me know if there are any other specific settings, or configuration values that would help narrow this down.

[vicentecr-uz]

Just commenting to say that I'm experiencing this as well and it's a little annoying.

[waydabber]

Generally BetterDisplay restores the app-last saved brightness when being opened. This is intentional. Isn't this what is happening?

You can change the relevant settings here:

Alternatively, if direct control and XDR upscaling is in effect, the app also sets its own brightness level, disregarding the system setting on startup.

[waydabber]

An other reason why the brightness may be pushed up/down on opening is this known macOS 27 Control Center issue (this is fixed in the latest v5.11 internal pre-release, try upgrading to that version by enabling internal pre-releases under Settings > Application > Updates):

#5846