shut down because of a problem message

That can be something running that didn’t handle the shutdown correctly.

There can be other causes, including hardware.

Download and run EtreCheck, and share the report to the clipboard. Then open a new reply here, and press the additional text button that looks like a printed page to get a text input box big enough to paste the hardware and software configuration report here, and paste and post it here.

I also get "shut down because of a problem" which is false -- I shut down completely using the drop-down menu. All else seems ok including start-up. This happens with and without a Storeva external drive attached.

Ventura 13.2.1 (22D68)

Jayne De Sesa wrote:

I also get "shut down because of a problem" which is false -- I shut down completely using the drop-down menu. All else seems ok including start-up. This happens with and without a Storeva external drive attached.

That usually means a crash somewhere during shutdown.

Which can be an add-on app (some add-on security apps can get tangled, for instance), or can be hardware, or can be a macOS bug.

You can post EtreCheck details here as requested above, or can contact Apple Support and discuss this with them.

I’d also suggest an update for Ventura as well (to 13.3.1), on the possibility that this is a Ventura bug.

Thank you, Mr. Hoffman. I'll update and see what happens. I don't like the looks of EtreCheck, I have CleanMyMac which includes security apps, and hopefully it's not a hardware problem. If this continues, I'll take the machine to a genius bar.

Remove CleanMyMac. Cleaning apps are unnecessary, and have caused issues over the years. Variously corruptions that have required re-installation. Use the vendor instructions to remove the app. Test again.

You are completely misplacing your trust. You are suspicious of a simple diagnostic utility, developed by a respected member of this community, and yet you gladly pay for something that is known around here by the not so nice but merited nickname of brickmymac...