Hard Sudoku rewards careful candidate tracking. The next move may come from a relationship between a 3×3 box and a row or column, rather than from an obvious empty cell.
Comfortable solvers looking for a longer, more deliberate puzzle.
Write candidates first. If all possible positions for one digit in a box lie on the same row, remove that digit from the rest of that row outside the box. This box-line interaction can reveal a single.
On a keyboard, use the arrow keys to move between cells and N to toggle notes. Read the beginner guide or try a worked naked-single example.