@AnnaAntifa@mastodon.nl where is 1 in box 4 (the middle box on the left)? In row 6. So 1 cannot be in the center box in row 6. This is one of the common tricks to get going - if a number can only be in one column or row in a particular box, then no other box can contain that number in the same column or row. I highly recommend watching the videos of the YouTube channel cracking the cryptic. Not only are the types of Sudoku these guys play way more fun, and they explain the logic really well, you also get to become a lot better at regular Sudoku rather than crunching through yet another one.