Brightness Slider Missing.

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Zeeshan678 wrote:

I m using MacBook Pro 2014. Last few days I face problem my Macbook Display Slider missing and brightness always full. its hurt my eyes.

I do SMC reset also reset NVRAM and PRAM But nothing Please solve my issue. if any one know.

https://discussions.apple.com/content/attachment/4cfcbaad-50da-4327-801b-0bb4f8fa78b0

Uninstall any and all third party Antivirus, Cleaners, Optimizers, VPN, speeder uppers....

To trouble shoot further you can:

—Try a SafeBoot https://support.apple.com/en-us/HT201262

Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc.

Login and test. Reboot as normal and test as caches get rebuilt.

In Safe mode third party system modifications and system accelerations are disabled, it removes malware, etc hampering smooth operation, however a reboot will put it back to normal mode.

This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.

—Test issue in another user (or guest user) account https://support.apple.com/guide/mac-help/set-up-other-users-on-your-mac-mtusr001/mac

This will tell you if it a universal issue or isolated to your user/admin account.