Partial Solution.
I have found the answer but not the cure. I guessed that it might have to do with updates because the last time I synced to the cloud with Sudoku was the 17 March 2024. Everyday for 7 days after it would not sync; it registered the game and when I switched it off and returned to it afterward it regressed to the previous score of zero. So today (25 March) I switched on my out of date laptop and stopped any automatic updates and played two games for the 18 March 2024, they both registered and remained the same after switch off. I returned to my up to date PC and played the final game for the 18th which showed me on the calendar check as a green ticked box. Switched it off, returned and it regressed to an unticked box. The moral of the story is that you have to play with an out of date Win11 to enable Sudoku until Microsoft awake from their deep slumber and check all the side effects of their improvements (tongue in cheek). I am now going to use my laptop to catch up with a weeks unsynced Sudoku. A Sudoku binge eh?
Further to the previous I have now caught up with all my Sudoku games on my laptop, I then tried it again on my up to date PC and it still doesn't sync. So in order not to lose my monthly input of Sudoku I will continue to use my laptop until Microsoft find out what they've done wrong on the 18 March. Maybe the next update will cure (tongue in cheek)?
Further to the previous paragraphs it is now May. I finished all March and Aprils Sudoku and unfortunately had to update my laptop so I no longer have a Sudoku facility on it any more. There have been a few Microsoft updates in this time and none of them have cured the problem. Therefore if I want to continue with Sudoku achievements and have a year of success I have no recourse but to go to the end of the garden and update my Sudoko on my win10 PC. The moral of the story is 'use a win10 to win'. I hope Microsoft get off their backsides for this before winter this year.