How do I restore accessibility contrast slider on MacBook Air?

Try looking here...

System Settings->Appearance->Liquid Glass->adjust slider to taste.

or here...

System Settings->Accessibility->Display->adjust display contrast to taste.

The contrast sider is not gone. It is in the same place it was before the update. If it’s not showing try restarting your MBA in Safe Mode.

Start up your Mac in safe mode - Apple Support

"I updated my software and the slider bar came back."

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Excellent job troubleshooting this!

A software update is a common fix.

I updated my software and the slider bar came back.

"How do I restore accessibility contrast slider on MacBook Air?: Accessibility contrast slider is gone and now it's way too dark. Help!"

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Report this Successful Fix to Apple:

Do your Part: Inform Apple of a successful fix from installing this update. Apple wont get back to you directly, but the more feedback thy receive from its users, the more they will know what issues existed, and what updates successfully fixed it.

1. Go Here: Feedback - MacBook Air - Apple
2. Select: "Feature Request" for the "Feedback Type"
3. Select: "[your Operating System]" for "Which operating system are you running?"
4. Select: "[your MacBook Air model]" for "What type of computer do you own?"
5. Comment: on what the issue is, and which an update was the solution. Include the URL of this thread.
6. Proceed from there as necessary

Thanks for commenting. The mac doesn't have a Liquid glass setting, and the display for contrast slider is gone...