... by: Frans Goosens#571
Combination 2-digits cells
C9=5 No solution, Undo calculation
C9=6 ( E7=1 ) Solved,
#571, December 9 - December 15, 2023:
WARNING: This is the Weekly 'Unsolvable' Sudoku, rated above 'Extreme'.
This is currently unsolvable by my solver, except perhaps with trial and error strategies.
Using the solver will not help you. (much).