Here we go - after a factory reset, I had to reconfigure everything.
This basically test git link tested again - -- --
So the initial problem was that when my laptop rebooted to 'factory reset' it started with windows 10 version 1511 (!) The .NET Framework was less than version 4.7 (which GitHub needs to communicate). Somehow, after many attempts, windows finally upgraded to version 21H1 which must have automatically upgraded the .NET Framework, since I just pushed this ReadMe.md from Rstudio.
Now the final test is to pull this to Rstudio and then commit and push the next amendment.....
...so a successful pull...and this amendment pushed to complete the confirmation.
And I might s well keep this for posterity.