Thank you so much for your patience and persistence as you helped me work though this. Our computer is clean and is much faster on startup/login than it had been.
Ran Delfix, which did its job.
Ran sfc /scannow. Result: Windows Resource Protection did not find any integrity violations
Ran powershell to reinstall Windows System apps, and restarted computer.
The Start menu problem is still with me, but it's low impact, so I'll put up with it unless it gets worse - I just have to keep restarting until it goes away, and it's only in the admin account, not the user account which is where we normally live and work.
I've reviewed and will use the guide to staying safer online - some I do already but some I need to start doing.
Have a great Chinese New Year of the chicken!
Best regards and thank you again,