Brightness adjustment is not available in Display settings

Start up your Mac in safe mode. It will do a Repair Disk, clear cache files and only load Apple Software, extensions and fonts. This will eliminate all third party software from loading. So, it will load slowly - normal. Once logged into computer run in this mode for say 10 - 15 minutes and Test if the Brightness Control function as expected. If Yes, then there might be some third party software interfering with the OS and / or there is an issue in the User Account of the computer.

Should the latter be the issue ( User Account ) try Set up users, guests, and groups on Mac only for testing purposes and Test the Brightness Controls in this account.

Luis Sequeira1 wrote:

AFAICT there is no brightness slider in System Preferences for laptops.

...

Sorry, incorrect. From my M1 MacBook Air and it is there whether

Default or scaled is selected:

As for the OP, I would set up an appointment at the Genius Bar

or an Authorized Apple Service Provider and have them take a

look at it. It seems almost like the system, for what ever reason,

is not properly detecting the internal display as the window you get

is sometimes typical of external displays that do not support

Mac control of brightness.

I have this too. Did this get resolved?

AFAICT there is no brightness slider in System Preferences for laptops.

What is surprising is that the controls in the touchbar are not working. Can you press command-shift-6 and post the resulting shot of the touchbar? It is saved to your Desktop by default.

Also: Please run Etrecheck and post its full report here.

Use the “additional text” button and paste the report into the text box.

As Learned Contributor @Luis Sequeira 1 mentioned. You experience is not normal at all.

Suggest downloading the Application Etrecheck directly from a Trusted Developer and well Respected ASC Contributor. The application is free or paid from added features. Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ). It will take a Snap Shot -  both the hardware and software. The Report will Not Reveal Any Personal Information. Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Firstly - No Time Machine Backup so flying without a Safety Net for sure. It could be very important before attempting any trouble shooting.

/Applications/Brightness Slider.app/Contents/Library/LoginItems/BSLoginLauncher.app - it is not going to help if Native Brightness is not functioning as expected.

biometrickitd - not 100% sure if this is a Native Apple Damon or not. Usually associated with Touch ID in iPhones ?

Have you read up on Use Control Center on Mac and use Native Brightness Controls instead of Third Party Software ?

Try…

Reset NVRAM or PRAM on your Mac - Apple Support

How to reset the SMC of your Mac - Apple Support

Thank you, wooodmeister50, for setting the record straight.

I was utterly convinced that it wasn't there... but you are right, it is. I should have checked!

Actually, that dialog really hasn't changed much since

my 17" PowerBook back in the old PowerPC days with

only an extra couple of checkboxes and tabs added

since then.