my computer will shot down when i pose for a while. Message: you can't use this computer until you instal a critical update. what should i do?

Maiga Said:

"Here is the message appearing on my computer.: A critical software update is required for your Mac, but an error was encountered while installing this update. Your Mac can't be used until this update is installed."

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Updating a Stuck Mac:

Reinstall the macOS:

Nothing would be lost. It's just that misplaced items would be placed back to where they should be and corrupt system files would be replaced by clean files. Go Here: Reinstall macOS - Apple Support. Use the third bulleted method: [command + r].  Important: Prior to installing an update or performing a reinstallation, to prevent data loss, be sure to Back up your Mac with Time Machine.

I find most times this indicates a hardware issue which is affecting the TouchBar. You can try reinstalling macOS over top of itself to see if it solves the problem (a couple people mentioned this solved their problem), otherwise you will likely need to have the laptop repaired.

In the mean time you should be able to boot into Safe Mode to continue using the laptop in a more limited fashion and to be able to make a backup of the computer if necessary.