After loading Catalina I can no longer change the screen brightness

Hello gbsales,

I understand you're no longer able to change the brightness of the display on your MacBook Pro after updating it to macOS Catalina. It's never expected to experience issues like this after updating your macOS version, so I can see why you would reach out for some assistance. I'm happy to help you.

To resolve this issue, I have some steps I recommend trying. These steps will troubleshoot what you're experiencing, as well as help in narrowing down the culprit. Test out adjusting the brightness on your Mac after each step. When you test it out, try out the various steps for adjusting brightness you see here: Change your Mac display’s brightness. If you're able to successfully adjust the brightness, make note of which steps you took when it worked for you (i.e., brightness function keys, System preferences, etc.).

1. Disconnect any devices/peripherals currently connected to your MacBook Pro other than the charger.
2. Enable "Automatically adjust brightness" in System Preferences > Display. This setting may also be listed as "Ambient light compensation." If it's already enabled, try disabling it and then testing your brightness again.
3. Restart your Mac.
4. Reset the SMC: How to reset the System Management Controller (SMC) on your Mac.
5. Adjust the brightness while booted into safe mode: Use safe mode to isolate issues with your Mac. Test the brightness once more after restarting your Mac and logging into your normal user account.
6. Test out your brightness while logged into a brand-new user account: Set up users, guests, and groups on Mac.

If the issue persists, respond back letting me know if you experienced it while booted in safe mode or in a new user account.

Thanks for using Apple Support Communities.

Take care!

Hello again gbsales,

It's wonderful to hear this is working for you now. Enjoy the rest of your week!

Cheers!