MacBook Pro 16-inch 2021 M1 Max won't stay off and keeps powering up on its own.

If you connect or disconnect any external devices after powering down the Mac, then it could trigger the Mac to power on again. This includes the power adapter charging cable.

If you touch any key on the built-in Keyboard or even the Trackpad, then it may cause the laptop to power on again. You would be surprise at how easy it is to accidentally brush a key or trackpad even when you are being careful.

Also, a faulty Lid Angle Sensor can cause these problems as well. Does the laptop go to sleep when the lid is nearly closed & wake once the lid is lifted maybe a 1/4" (peek at the screen as you slowly close the lid)?

macuser_1999 wrote:

I have a MacBook Pro 16-inch, 2021, Apple M1 Max. Whenever I shut it down, it restarts on its own without any interaction with it. Is there a way to keep it shut down?

you do not paint a very big picture....

Verify your software is up to date…

The current stable release of Sequoia including bug fixes, security updates is macOS 15.5

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

A SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

Login and test. Reboot as normal and test. Caches get rebuilt automatically.

if you ever used/scheduled repeating automatic logout or login time setting...?

From Terminal.app you cancel these settings manually, copy and paste:

sudo pmset repeat cancel

You can refresh your understanding of log out, sleep, wake, restart or shut down your Mac, review:

Shut down or restart your Mac - Apple Support

for the open/close sensor, you can run the user hardware diagnostic if you suspect an issue:

Use Apple Diagnostics to test your Mac - Apple Support