you made a mistake at R9C4 possible candidates should be 579 and 6 can not be there since 6 is already in that box but this sudoku also requires some advanced sudoku techniques like colouring, XYZ Wing,X-Y Chain. In Completion Even the world best sudoku solver's guess in such kind of puzzles they just wait a few seconds if they dont get any clue they just guess at that point some even guess multiple times.