Extreme Sudoku is the longest challenge here. Expect to work across the whole board and maintain accurate candidates as the puzzle unfolds.
Solvers who enjoy advanced elimination and are comfortable taking their time.
Start with complete candidate notes. After singles and pairs, compare candidate positions across rows and columns. If a pattern is uncertain, use a hint instead of guessing and inspect why that placement works.
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.