A Medium 11×11 Puzzle Solved with Shape Squeeze in 21 Steps

This 11×11 board rates as medium (difficulty score 840). Solving it from scratch takes 21 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Paired regions, Shape squeeze. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
2. Next, every open cell left in this region sits in column K, so its marker has to land there; that clears every other open cell in the column.
3. Then, every open cell left in this region sits in row 8, so its marker has to land there; that clears every other open cell in the row.
4. After that, together, two regions have open cells only in columns I and J; with one marker each, those two markers have to fill exactly those two columns, so every other region's open cells there can be cleared.
5. Now, place a marker at H9. Region has exactly one open cell left. Placing here clears the rest of row 9, column H, and its region. Placing here also clears its 2 touching neighbours.
6. From there, place a marker at J8. Region has exactly one open cell left. Placing here clears the rest of row 8, column J, and its region.
7. Following that, every open cell left in this region sits in row 7, so its marker has to land there; that clears every other open cell in the row.
8. First, together, two regions have open cells only in columns F and G; with one marker each, those two markers have to fill exactly those two columns, so every other region's open cells there can be cleared.
9. Next, every open cell left in this region sits in row 11, so its marker has to land there; that clears every other open cell in the row.
10. Then, every open cell left in this region sits in row 10, so its marker has to land there; that clears every other open cell in the row.
11. After that, place a marker at E6. Region has exactly one open cell left. Placing here clears the rest of row 6, column E, and its region. Placing here also clears its 2 touching neighbours.
12. Now, place a marker at G7. Region has exactly one open cell left. Placing here clears the rest of row 7, column G, and its region.
13. From there, place a marker at F1. Region has exactly one open cell left.
14. Following that, place a marker at D11. Region has exactly one open cell left. Placing here clears the rest of row 11, column D, and its region. Placing here also clears its 1 touching neighbour.
15. First, place a marker at A10. Region has exactly one open cell left. Placing here clears the rest of row 10, column A, and its region.
16. Next, every open cell left in this region sits in column C, so its marker has to land there; that clears every other open cell in the column.
17. Then, every remaining candidate in this region touches B4 and B5, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
18. After that, place a marker at C4. Row 4 has exactly one open cell left. Placing here clears the rest of row 4, column C, and its region. Placing here also clears its 1 touching neighbour.
19. Now, place a marker at B2. Region has exactly one open cell left. Placing here clears the rest of row 2, column B, and its region.
20. From there, place a marker at K3. Region has exactly one open cell left. Placing here clears the rest of row 3, column K, and its region.
21. Finally, place a marker at I5. Region has exactly one open cell left.

The key move here was Shape squeeze. Once you can spot that, this board falls quickly. ∎