A Hard 11×11 Puzzle Solved with Forced Chain in 23 Steps

This 11×11 board rates as hard (difficulty score 1032). Solving it from scratch takes 23 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region 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 remaining candidate in this region touches J2 and K2, 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 J4, 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 I3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
5. Now, 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.
6. From there, every remaining candidate in this region touches B10, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
7. Following that, if K1 were the marker, it would force A5, B5, C5, and 5 more cleared (every open cell left in this region sits in row 5, so its marker has to land there), then H4 (the last open cell in region 6), then J5 (the last open cell in region 5), and region 8 would end up with no open cell for its marker, which can't happen. So it can't go there.
8. First, place a marker at J1. Region has exactly one open cell left. Placing here clears the rest of row 1, column J, and its region. Placing here also clears its 1 touching neighbour.
9. Next, place a marker at I4. Region has exactly one open cell left. Placing here clears the rest of row 4, column I, and its region. Placing here also clears its 2 touching neighbours.
10. Then, 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.
11. After that, place a marker at H6. Region has exactly one open cell left. Placing here clears the rest of row 6, column H, and its region. Placing here also clears its 2 touching neighbours.
12. Now, place a marker at F5. Region has exactly one open cell left. Placing here clears the rest of row 5, column F, and its region.
13. 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.
14. Following that, 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.
15. First, every open cell left in this region sits in row 9, so its marker has to land there; that clears every other open cell in the row.
16. Next, together, two regions have open cells only in columns E 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.
17. Then, every open cell left in this region sits in column D, so its marker has to land there; that clears every other open cell in the column.
18. After that, place a marker at C8. Region has exactly one open cell left. Placing here clears the rest of row 8, column C, and its region. Placing here also clears its 1 touching neighbour.
19. Now, place a marker at A7. Region has exactly one open cell left. Placing here clears the rest of row 7, column A, and its region.
20. From there, place a marker at B11. Region has exactly one open cell left. Placing here clears the rest of row 11, column B, and its region.
21. Following that, place a marker at D10. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
22. First, place a marker at G9. Region has exactly one open cell left. Placing here clears the rest of row 9, column G, and its region.
23. Finally, place a marker at E2. Region has exactly one open cell left.

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