Previous shutdown cause: -20

Previous Shutdown cause:

-20 BridgeOS T2-initiated shutdown.

The T2 chip in your 2018+ MacBook Pro or other Mac (list in link) initiated a shutdown.

SYSTEM Error -20 is indeed a Write I/O Error, but Previous Shutdown Causes are distinct. Gorge Garside collected a list, here:

https://georgegarside.com/blog/macos/shutdown-causes/

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vinayakagarwal A Said:

"Previous shutdown cause: -20: My Mac unexpectedly shut down, and I obtained the previous shutdown cause from Terminal which was -20. What does it refer to? Its a 2.3 GHz 8-Core Intel Core i9 MacBook Pro"

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Troubleshooting Previous shutdown cause: -20:

Verify the Condition of your Mac’s Battery

To do so...

1. Go to: Apple menu
2. Select: About This Mac
3. Click: System Report button
4. Select: Hardware on the far-left
5. Select: Power
6. View: Battery Information
7. View: Health Information
8. View: Condition

What does it read?***

***Screenshot:

Personal information blocked out.

vinayakagarwal Sad:

"This is the information. To keep in mind: I keep my Mac almost always plugged in and charging."

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Thank you for the screenshot.

What does it read for Battery Health?

To Find Out:

1. Go to: Apple menu
2. Hold Down: Option button
3. Click: System Information...
4. Select: Hardware on the far-left
5. Select: Power
6. View: Battery Information
7. View: Health Information
8. View: Maximim Capacity

Error code -20 is listed as a Write Error. Were you using Terminal at the time of the crash?

T2 handles battery and power, and also security and encryption, and part of Sound processing, and the fingerprint sensor, according to this glossy article:

https://www.howtogeek.com/677167/what-does-apples-t2-security-chip-do-in-your-mac/

Relevant discussion: https://discussions.apple.com/thread/251506850