Magic keyboard backlight not working on MacBook

Hello Pheerawat,

Welcome to Apple Support Communities! We're happy to provide some information to help you with the Magic Keyboard issue you're experiencing.

Give the steps in the article below a try for help turning the Magic Keyboard on or off.

Turn your Mac keyboard’s backlighting on or off

We also recommend trying to start up in safe mode and see if that helps with the keyboard backlight. This step may resolve the issue if it is related to the startup items, but if it does not, it will help us greatly isolate the cause. Safe mode will tell us if the issue is related to a startup item, third party plugins, caches, fonts. 

Once inside safe mode, log in to your account and check if the issue is also occurring or not. Use this article for the steps to get into safe mode: How to use safe mode on your Mac

If everything is working properly in safe mode, but then is not working after you restart the Mac, please check the section titled "If an issue doesn't happen in safe mode" for the next troubleshooting steps. 

If the issue is also happening in safe mode, you will need to see if this problem occurs in a new test administrator account on your Mac. A test user will let us know if the issue is isolated to your account, or system wide. 

Change Users & Groups settings on Mac

If the issue is being experienced in the test user also, then please check the section titled "If the issue happens in the other account". 

Let us know if you have any questions.

Thank you for using Apple Support Communities.

Take care!