Sudoku 2024 09 23 hard

Back to my usual times, maybe?
Play it: sudokupad.app/...

[@rickschaut8366]

Once you found the hidden single 9 in r3, c3, that meant that the 5 in r1 could only be in box (region) 1. That means that the only place for a 5 in column 4 was row 8. That, in turn, places the 6 in r6, c8, because the 6 in row 8 could only go in box 8.