How to solve this 9×9 logic puzzle

9×9 · steady · 12 steps

This 9×9 board rates as steady (difficulty score 552). Solving it from scratch takes 24 logical steps, using 5 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement. Every step below is forced — nothing here is a guess.

First, place a marker at row 1, column 9. Region has exactly one open cell left. Placing here clears the rest of row 1, column 9, and its region. Placing here also clears its 1 touching neighbour.
Next, place a marker at row 9, column 4. Region has exactly one open cell left. Placing here clears the rest of row 9, column 4, and its region. Placing here also clears its 2 touching neighbours.
Then, every open cell left in this region sits in row 8, so its marker has to land there — clearing every other open cell in the row.
After that, place a marker at row 7, column 3. Region has exactly one open cell left. Placing here clears the rest of row 7, column 3, and its region. Placing here also clears its 1 touching neighbour.
Now, every open cell in column 2 belongs to the same region, so that region's marker has to be somewhere in this column — clearing every other open cell in the region.
From there, place a marker at row 2, column 1. Column 1 has exactly one open cell left. Placing here clears the rest of row 2, column 1, and its region. Placing here also clears its 1 touching neighbour.
Following that, every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row — clearing every other open cell in the region.
First, place a marker at row 4, column 2. Row 4 has exactly one open cell left. Placing here clears the rest of row 4, column 2, and its region.
Next, place a marker at row 6, column 5. Column 5 has exactly one open cell left. Placing here clears the rest of row 6, column 5, and its region.
Then, place a marker at row 5, column 8. Region has exactly one open cell left. Placing here clears the rest of row 5, column 8, and its region.
After that, place a marker at row 3, column 7. Region has exactly one open cell left. Placing here clears the rest of row 3, column 7, and its region.
Finally, place a marker at row 8, column 6. Region has exactly one open cell left.

The key move here was Line confinement — once you can spot that, this board falls quickly. ∎