Sigh....
I performed all the many steps outlined in your instructions above. Virus software removal , deep virus scans, disk integrity scans, etc.- everything - then finally a Windows 11 Install/Repair. When the system booted up after the repair/upgrade the problem was not there. But, and I was dreading this, when I rebooted the problem reappeared. Definitely at wits end after all this time over many weeks. During these boots all startup processes were disabled in TM, leftover from my testing.
Anyway, as part of that troubleshooting process I did the msconfig process of eliminating services, and startup programs in various combinations, and there were a number of times when the problem went away. Always when some combination of services and/or startup programs were disabled. However, I believe that there are some subtleties to msconfig that I need to figure out. Like in msconfig Selective boot if you specify load startups, but in TM all the startups are disabled, what actually happens. Or if you specify Load Services, do the ones you've disabled in msconfig start anyway, or does it honor the services status.
It also looks like the msconfig boot settings persist through restarts. But I wonder if there was something different about the restart after the upgrade repair that disabled the problem. There are a lot of different combinations of Selective load options, service status and startup applications, and I'm not sure I have understood all the implications of the various combinations of these.
I'm exhausted. I've been working on this problem for weeks, sometimes for 10 hours a day being retired. So I need to step away for a day or so. Please do not go away. If I need to post giberish to keep this thread open, let me know.