An Expert 11×11 Puzzle Solved with Forced Chain in 34 Steps

This 11×11 board rates as expert (difficulty score 1466). Solving it from scratch takes 34 logical steps, using 8 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Paired regions, Shape squeeze, Forced chain. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in column H, so its marker has to land there; that clears every other open cell in the column.
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, together, two regions have open cells only in rows 1 and 2; with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
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, every remaining candidate in this region touches I4 and J4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
6. From there, every remaining candidate in this region touches G4, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
7. Following that, every remaining candidate in this region touches E9, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
8. First, if A3 were the marker, it would force J5 (the last open cell in region 4), and column I would end up with no open cell for its marker, which can't happen. So it can't go there.
9. Next, that one can't be the marker: at B3 it would force J5 (the last open cell in region 4), and column I would be left with no open cell for its marker.
10. Then, marking C3 would force J5 (the last open cell in region 4), and then column I would be left with no open cell for its marker. So C3 can't be the marker there.
11. After that, if D3 were the marker, it would force J5 (the last open cell in region 4), and column I would end up with no open cell for its marker, which can't happen. So it can't go there.
12. Now, that one can't be the marker: place it at E3, and row 4 would be left with no open cell for its marker.
13. From there, every remaining candidate in this region touches B5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
14. Following that, marking F3 would force J5 (the last open cell in region 4), and then column I would be left with no open cell for its marker. So F3 can't be the marker there.
15. First, if G3 were the marker, it would force H1 (the last open cell in region 3), then K2 (the last open cell in region 5), then J5 (the last open cell in region 4), and column I would end up with no open cell for its marker, which can't happen. So it can't go there.
16. Next, place a marker at F4. Region has exactly one open cell left. Placing here clears the rest of row 4, column F, and its region. Placing here also clears its 2 touching neighbours.
17. Then, place a marker at A5. Region has exactly one open cell left. Placing here clears the rest of row 5, column A, and its region. Placing here also clears its 1 touching neighbour.
18. After that, together, two regions have open cells only in rows 6 and 7; with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
19. Now, every open cell left in this region sits in column B, so its marker has to land there; that clears every other open cell in the column.
20. From there, every open cell in column C belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
21. Following that, every remaining candidate in this region touches C9 and C10, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
22. First, if C8 were the marker, it would force B10 (the last open cell in region 8), and region 11 would end up with no open cell for its marker, which can't happen. So it can't go there.
23. Next, place a marker at C11. Region has exactly one open cell left. Placing here clears the rest of row 11, column C, and its region. Placing here also clears its 2 touching neighbours.
24. Then, place a marker at B9. Region has exactly one open cell left. Placing here clears the rest of row 9, column B, and its region.
25. After that, if K1 were the marker, it would force H2 (the last open cell in region 3), then J3 (the last open cell in region 4), then I6 (the last open cell in region 7), and the chain continues, and row 10 would end up with no open cell for its marker, which can't happen. So it can't go there.
26. Now, place a marker at K2. Region has exactly one open cell left. Placing here clears the rest of row 2, column K, and its region. Placing here also clears its 1 touching neighbour.
27. From there, place a marker at H1. Region has exactly one open cell left.
28. Following that, place a marker at I3. Region has exactly one open cell left. Placing here clears the rest of row 3, column I, and its region.
29. First, if G6 were the marker, it would force J7 (the last open cell in region 7), then E8 (the last open cell in region 9), and row 10 would end up with no open cell for its marker, which can't happen. So it can't go there.
30. Next, if J6 were the marker, it would force G7 (the last open cell in region 6), then E8 (the last open cell in region 9), and row 10 would end up with no open cell for its marker, which can't happen. So it can't go there.
31. Then, place a marker at J7. Region has exactly one open cell left. Placing here clears the rest of row 7, column J, and its region.
32. After that, place a marker at D6. Region has exactly one open cell left. Placing here clears the rest of row 6, column D, and its region.
33. Now, place a marker at E10. Region has exactly one open cell left. Placing here clears the rest of row 10, column E, and its region.
34. Finally, place a marker at G8. Region has exactly one open cell left.

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