Why does my Mac Studio automatically shut down?

It seems that there may be a schedule shutdown set.

Run this command in Terminal:

pmset -g sched

and tell us what the output is.

If you want to cancel these recurring events:

sudo pmset repeat cancel

You will be asked for your password. There is no feedback as you type it, that is normal. Press enter.

Then you can run

pmset -g sched 

to confirm that they are gone.

From what I can tell there isn't an easy way to get a Mac to shut down completely automatically. Perhaps using a third party utility, yes, or using Terminal. Are you sure it is shutting down and not just sleeping? Settings > Energy, and Settings > Lock Screen are where I would look to do that.

If it is truly shutting down then it could be something more significant such as power failures.

That pmset command is the Terminal command to which I was referring. It would be a very intentional thing to set, with familiarity with Terminal use so I figured if you had done it that simply mentioning Terminal would ring a bell. If this is a work computer, make sure the IT department didn't add this feature. If it's a home computer, make sure somebody didn't come into the room and temporarily unplug your computer to use the vacuum cleaner or something.

I know that other Apple hardware will shut down if it overheats. Not sure how that would happen with a desktop model unless you have it directly in front of a heat vent or your cat sleeps on it. Still worth noting. I bought a little stand for my mini which keeps it a few inches off my desk and ensures better airflow.

Since it appears that pmset was configured, somebody must have had access to, or ownership of, this computer before you did if you did not set it. In that case there could be other surprises waiting for you.