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

This 11×11 board rates as expert (difficulty score 1420). Solving it from scratch takes 30 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 row 1, so its marker has to land there; that clears every other open cell in the row.
2. Next, every open cell in column A 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.
3. Then, if H1 were the marker, it would force G3 (the last open cell in region 5), then A2, J2 and K2 cleared (every open cell left in this region sits in row 2, so its marker has to land there), then A4, B4, C4, and 3 more cleared (every open cell left in this region sits in row 4, so its marker has to land there), and region 6 would end up with no open cell for its marker, which can't happen. So it can't go there.
4. After that, that one can't be the marker: at A2 it would force F3 (the last open cell in region 1), then H4 (the last open cell in region 5), and region 3 would be left with no open cell for its marker.
5. Now, if C2 were the marker, it would force A3, E3, A4, and 6 more cleared (together, two regions have open cells only in rows 3 and 4), then A5, D5, E5, and 4 more cleared (every open cell left in this region sits in row 5, so its marker has to land there), then G1, G6, G7, and 10 more cleared (together, two regions have open cells only in columns G and H), and the chain continues, and region 9 would end up with no open cell for its marker, which can't happen. So it can't go there.
6. From there, every remaining candidate in this region touches E3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
7. Following that, marking E2 would force A3, B3, C3, and 7 more cleared (together, two regions have open cells only in rows 3 and 4), then A5, C5, D5, and 4 more cleared (every open cell left in this region sits in row 5, so its marker has to land there), then G1, G6, G7, and 10 more cleared (together, two regions have open cells only in columns G and H), and the chain continues, and then region 10 would be left with no open cell for its marker. So E2 can't be the marker there.
8. First, if F2 were the marker, it would force H5, H6, H7, and 4 more cleared (every open cell left in this region sits in column H, so its marker has to land there), then A3, B3, C3, and 8 more cleared (together, two regions have open cells only in rows 3 and 4), then G5 (the last open cell in region 6), 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.
9. Next, that one can't be the marker: place it at G2, and region 1 would be left with no open cell for its marker.
10. Then, marking H2 would force F3 (the last open cell in region 1), then J1 (the last open cell in region 2), then I4 (the last open cell in region 3), and the chain continues, and then region 7 would be left with no open cell for its marker. So H2 can't be the marker there.
11. After that, marking J1 would force D2 (the last open cell in row 2), then A3, B3, A4, and 6 more cleared (together, two regions have open cells only in rows 3 and 4), then A5, C5, E5, and 3 more cleared (every open cell left in this region sits in row 5, so its marker has to land there), and the chain continues, and then region 10 would be left with no open cell for its marker. So J1 can't be the marker there.
12. Now, if I2 were the marker, it would force F3 (the last open cell in region 1), then G1 (the last open cell in region 2), then J4 (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.
13. 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.
14. Following that, marking G1 would force H5, H6, H7, and 4 more cleared (every open cell left in this region sits in column H, so its marker has to land there), then A3, F3, I3, and 6 more cleared (together, two regions have open cells only in rows 3 and 4), then D2 (the last open cell in region 1), and then region 3 would be left with no open cell for its marker. So G1 can't be the marker there.
15. First, that one can't be the marker: at J2 it would force F1 (the last open cell in region 2), and region 1 would be left with no open cell for its marker.
16. Next, marking K2 would force F3 (the last open cell in region 1), then I1 (the last open cell in region 2), then H4 (the last open cell in region 5), and then region 6 would be left with no open cell for its marker. So K2 can't be the marker there.
17. Then, place a marker at D2. Row 2 has exactly one open cell left. Placing here clears the rest of row 2, column D, and its region. Placing here also clears its 1 touching neighbour.
18. After that, together, two regions have open cells only in rows 3 and 4; 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 row 5, so its marker has to land there; that clears every other open cell in the row.
20. From there, together, two regions have open cells only in columns G and H; 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.
21. Following that, place a marker at I6. Region has exactly one open cell left. Placing here clears the rest of row 6, column I, and its region. Placing here also clears its 2 touching neighbours.
22. First, place a marker at F1. Region has exactly one open cell left. Placing here clears the rest of row 1, column F, and its region.
23. Next, place a marker at G5. Region has exactly one open cell left. Placing here clears the rest of row 5, column G, and its region. Placing here also clears its 1 touching neighbour.
24. Then, place a marker at H3. Region has exactly one open cell left. Placing here clears the rest of row 3, column H, and its region.
25. After that, place a marker at J4. Region has exactly one open cell left. Placing here clears the rest of row 4, column J, and its region.
26. Now, place a marker at B10. Column 2 has exactly one open cell left. Placing here clears the rest of row 10, column B, and its region. Placing here also clears its 2 touching neighbours.
27. From there, 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.
28. Following that, place a marker at C7. Region has exactly one open cell left. Placing here clears the rest of row 7, column C, and its region.
29. First, place a marker at A8. Region has exactly one open cell left. Placing here clears the rest of row 8, column A, and its region.
30. Finally, place a marker at K9. Region has exactly one open cell left.

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