OP here. Reply for everyone interested in this thread.
Where I ended up and why.
Short story: I copy and pasted manually all old entries to Mozilla Thunderbird and then I could finally make a backup file (ics).
A little surprised being timed out for MS attention. Noting this in one reply above:
The synchronization is specific to Microsoft services.
I was, halfheartedly, going to ask if using an MS "owned" email would help. I never used the "Mail" app (start menu search "mail") but I also read somewhere giving an email to the app its nearly impossible to "ungive" it. Overall copying manually seemed less hassle.
Since my last post I learned of [ics files](https://en.wikipedia.org/wiki/ICalendar "en.wikipedia.org"). ICS goes back to 1998 and is widely supported. By Wiki "[Windows Calendar app](https://en.wikipedia.org/wiki/Calendar_%28Windows%29#History "en.wikipedia.org")" in current form go back to Windows Vista (2006) and did support ics files. ICS file support went away with Win 8. Added back with "Windows 10 Anniversary Update"??? I've been told this thread there is no backup option and I never found one, ICS or otherwise.
How did I, step by step, get my entries back?
I found this partially helpful:
>*6. Possible Workaround:*
- *While you can’t directly connect the taskbar calendar to New Outlook, consider using the Windows Calendar app as an intermediary:*
- *Open the Windows Calendar app (search for it in the Start menu).*
- *Add your events there, and they should sync with your Gmail account (since you’ve noticed that New Outlook entries appear in your Gmail calendar).*
- *This way, you can still have a convenient way to add items via the tray icon clock calendar.*
My events came back in the CLOCK TRAY calendar but never showed up in either G-Mail or New Outlook.
**Steps:**
\* **** Found and started "Calendar" from the Start menu.
\* Adding an event in "Calendar" app and suddenly all TRAY CLOCK events were back but nota bene, not back in the "Calendar" app. TRAY CLOCK **SAVE**, **MORE DETAILS** buttons also un-greyed and active again.
\* From TRAY CLOCK selecting every date from my last Win 10 reinstall (July 2022 ~600 dates)
\* Clicking on every event in TRAY CLOCK thus starting the "Calendar" app, gave every detail of each event which I then copy pasted, one at a time, into Mozilla ThunderBird.
Note 1, as noted above I found repeating **Right-Arrow + Enter** the fastest way to go through all dates.
Note 2, If multiple events in one day, TRAY CLOCK clicking one event does not copy the others, every event must be individually clicked (opened in Calendar app)
Note 3, Calendar app seems flimsy, going back two weeks later much of Calendar app was empty again *but everything was still available accessing from the TRAY CLOCK*. So I ended up selecting the 600 dates a second time, this time copying each event to Mozilla ThunderBird.
Mozilla Thunderbird looks good for now. What I like about it beyond the immediate need of creating an ics backup:
- free
- Open source = many eyes on code
- local backup support (ics), a deal killer for any app.
- keeping things local, no cloud unless I want to.
- search and list features not present in Win Cal app.
Its very similar to Win Cal app, except better and does not go away December 31 2024.