An Expert 11×11 Puzzle Solved with Forced Chain in 29 Steps

This 11×11 board rates as expert (difficulty score 1346). Solving it from scratch takes 29 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 3, 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 J2 and K2 and J4 and K4, 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, every remaining candidate in this region touches E10, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
5. Now, marking A1 would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and then region 8 would be left with no open cell for its marker. So A1 can't be the marker there.
6. From there, if B1 were the marker, it would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and region 8 would end up with no open cell for its marker, which can't happen. So it can't go there.
7. Following that, that one can't be the marker: at C1 it would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and region 8 would be left with no open cell for its marker.
8. First, marking D1 would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and then region 8 would be left with no open cell for its marker. So D1 can't be the marker there.
9. Next, if E1 were the marker, it would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and region 8 would end up with no open cell for its marker, which can't happen. So it can't go there.
10. Then, that one can't be the marker: at F1 it would force I2 (the last open cell in region 3), and region 4 would be left with no open cell for its marker.
11. After that, marking G1 would force I2 (the last open cell in region 3), then F4 (the last open cell in region 4), then K3 (the last open cell in region 5), and the chain continues, and then region 8 would be left with no open cell for its marker. So G1 can't be the marker there.
12. Now, if H1 were the marker, region 3 would end up with no open cell for its marker, which can't happen. So it can't go there.
13. From there, every open cell in row 1 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, marking J1 would force K3 (the last open cell in region 5), then I4, I5, I6, and 3 more cleared (every open cell left in this region sits in column I, so its marker has to land there), then H2, H4, H5, and 3 more cleared (every open cell left in this region sits in column H, so its marker has to land there), and the chain continues, and then column F would be left with no open cell for its marker. So J1 can't be the marker there.
15. First, if K1 were the marker, it would force J3 (the last open cell in region 5), then I5, I6, I9, and 2 more cleared (every open cell left in this region sits in column I, so its marker has to land there), then H2, H4, H5, and 3 more cleared (every open cell left in this region sits in column H, so its marker has to land there), and the chain continues, and column F 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 I1. Region has exactly one open cell left. Placing here clears the rest of row 1, column I, and its region. Placing here also clears its 1 touching neighbour.
17. 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. Placing here also clears its 2 touching neighbours.
18. After that, 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.
19. Now, 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.
20. From there, every open cell left in this region sits in column G, so its marker has to land there; that clears every other open cell in the column.
21. Following that, every open cell left in this region sits in column F, so its marker has to land there; that clears every other open cell in the column.
22. First, place a marker at D2. Region has exactly one open cell left. Placing here clears the rest of row 2, column D, and its region.
23. Next, place a marker at G4. Region has exactly one open cell left. Placing here clears the rest of row 4, column G, and its region. Placing here also clears its 1 touching neighbour.
24. Then, place a marker at E11. Region has exactly one open cell left. Placing here clears the rest of row 11, column E, and its region. Placing here also clears its 1 touching neighbour.
25. After that, place a marker at F9. Region has exactly one open cell left. Placing here clears the rest of row 9, column F, and its region.
26. Now, place a marker at H8. Region has exactly one open cell left. Placing here clears the rest of row 8, column H, and its region.
27. From there, place a marker at C6. Region has exactly one open cell left. Placing here clears the rest of row 6, column C, and its region. Placing here also clears its 1 touching neighbour.
28. Following that, 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.
29. Finally, place a marker at B10. Region has exactly one open cell left.

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