An Expert 11×11 Puzzle Solved with Forced Chain in 30 Steps

This 11×11 board rates as expert (difficulty score 1304). Solving it from scratch takes 30 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, 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 row 2, so its marker has to land there; that clears every other open cell in the row.
2. Next, every remaining candidate in this region touches J1 and K1 and J3 and K3, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
3. Then, every remaining candidate in this region touches J8, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
4. After that, if B1 were the marker, it would force D4, E4, F4, and 9 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and region 11 would end up with no open cell for its marker, which can't happen. So it can't go there.
5. Now, that one can't be the marker: at C1 it would force D4, E4, F4, and 9 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and row 8 would be left with no open cell for its marker.
6. From there, marking D1 would force B6, G6, H6, and 3 more cleared (every open cell left in this region sits in row 6, so its marker has to land there), then E4, F4, G4, and 7 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), and then row 5 would be left with no open cell for its marker. So D1 can't be the marker there.
7. Following that, if E1 were the marker, it would force D4, F4, G4, and 7 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and column H would end up with no open cell for its marker, which can't happen. So it can't go there.
8. First, that one can't be the marker: at F1 it would force D4, E4, G4, and 7 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and region 11 would be left with no open cell for its marker.
9. Next, marking G1 would force D4, E4, F4, and 7 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and then region 11 would be left with no open cell for its marker. So G1 can't be the marker there.
10. Then, if H1 were the marker, it would force D4, E4, F4, and 6 more cleared (every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row), then K4 (the last open cell in row 4), then J2 (the last open cell in region 3), and the chain continues, and region 7 would end up with no open cell for its marker, which can't happen. So it can't go there.
11. After that, that one can't be the marker: at I1 it would force K2 (the last open cell in region 3), then J7 (the last open cell in region 8), and region 4 would be left with no open cell for its marker.
12. Now, place a marker at A1. Row 1 has exactly one open cell left. Placing here clears the rest of row 1, column A, and its region.
13. From there, every open cell in row 3 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
14. Following that, place a marker at K4. Row 4 has exactly one open cell left. Placing here clears the rest of row 4, column K, and its region.
15. First, place a marker at J2. Region has exactly one open cell left. Placing here clears the rest of row 2, column J, and its region. Placing here also clears its 1 touching neighbour.
16. Next, place a marker at D5. Row 5 has exactly one open cell left. Placing here clears the rest of row 5, column D, and its region.
17. Then, every open cell left in this region sits in column I, so its marker has to land there; that clears every other open cell in the column.
18. After that, 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.
19. Now, every open cell in row 6 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
20. From there, every open cell in column E 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 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.
22. First, place a marker at B6. Column 2 has exactly one open cell left. Placing here clears the rest of row 6, column B, and its region.
23. Next, every remaining candidate in this region touches H7 and H8, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
24. Then, 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 3 touching neighbours.
25. After that, place a marker at I7. Region has exactly one open cell left.
26. Now, place a marker at C8. Row 8 has exactly one open cell left. Placing here clears the rest of row 8, column C, and its region.
27. From there, every remaining candidate in this region touches F10 and F11, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
28. Following that, place a marker at G11. Region has exactly one open cell left. Placing here clears the rest of row 11, column G, and its region.
29. First, place a marker at F3. Region has exactly one open cell left.
30. Finally, place a marker at E10. Region has exactly one open cell left.

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