After wasting almost 40 minutes on this
I go on to suduko solutions and see :
Step 11: Brute Force
The remainder of this puzzle was not solved by logic. This is because of solver limitations. It does not mean there is not a logical solution to this puzzle.
So needs trial and error at the end, so annoying, would have thought the app would only generate puzzles that each box can be solved by logical steps without trial and error ...
Central row is 3 2 6 4 (78) 1 (59) (59) (78) by logic
This makes cell R4C7 (78) by logic and there appear to be more available moves to follow those.
I have never seen this method before and I usually solve the hard ones and the odd expert ...
Can someone explain what is going on here ? What's this X wing thing ?