An Expert 9×9 Puzzle Solved with Forced Chain in 32 Steps

This 9×9 board rates as expert (difficulty score 1500). Solving it from scratch takes 32 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 remaining candidate in this region touches E2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
2. Next, marking A1 would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G2, C3, D3, and 3 more cleared (together, two regions have open cells only in rows 2 and 3), then I4, C5, G5, and 1 more cleared (together, two regions have open cells only in rows 4 and 5), and the chain continues, and then region 5 would be left with no open cell for its marker. So A1 can't be the marker there.
3. Then, if B1 were the marker, it would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G2, A3, C3, and 4 more cleared (together, two regions have open cells only in rows 2 and 3), then A4, I4, A5, and 3 more cleared (together, two regions have open cells only in rows 4 and 5), and the chain continues, and region 5 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 C1 it would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G2, A3, D3, and 3 more cleared (together, two regions have open cells only in rows 2 and 3), then A4, I4, A5, and 2 more cleared (together, two regions have open cells only in rows 4 and 5), and the chain continues, and region 5 would be left with no open cell for its marker.
5. Now, marking D1 would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G2, A3, C3, and 3 more cleared (together, two regions have open cells only in rows 2 and 3), then A4, I4, A5, and 3 more cleared (together, two regions have open cells only in rows 4 and 5), and the chain continues, and then region 5 would be left with no open cell for its marker. So D1 can't be the marker there.
6. From there, marking G1 would force F3 (the last open cell in region 2), then H6, H7, H8, and 1 more cleared (every open cell left in this region sits in column H, so its marker has to land there), then I8 and I9 cleared (every open cell left in this region sits in column I, so its marker has to land there), and the chain continues, and then row 9 would be left with no open cell for its marker. So G1 can't be the marker there.
7. Following that, if H1 were the marker, it would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G5, G6, G7, and 2 more cleared (every open cell left in this region sits in column G, so its marker has to land there), then I8 and I9 cleared (every open cell left in this region sits in column I, so its marker has to land there), and the chain continues, and row 9 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 I1 it would force F4, F5, F6, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then G7, G8, G9, and 3 more cleared (together, two regions have open cells only in columns G and H), then A7, B7, A9, and 4 more cleared (every open cell in row 8 belongs to the same region, so that region's marker has to be somewhere in this row), and row 9 would be left with no open cell for its marker.
9. Next, 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.
10. Then, every remaining candidate in this region touches H3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
11. After that, that one can't be the marker: at A2 it would force I3 (the last open cell in region 3), then G7, G8, G9, and 3 more cleared (together, two regions have open cells only in columns G and H), then B7, B8, C8, and 2 more cleared (every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row), and the chain continues, and row 7 would be left with no open cell for its marker.
12. Now, marking B2 would force I3 (the last open cell in region 3), then G7, G8, G9, and 3 more cleared (together, two regions have open cells only in columns G and H), then A7, A8, C8, and 2 more cleared (every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row), and the chain continues, and then row 7 would be left with no open cell for its marker. So B2 can't be the marker there.
13. From there, if C2 were the marker, it would force I3 (the last open cell in region 3), then G7, G8, G9, and 3 more cleared (together, two regions have open cells only in columns G and H), then A7, B7, A8, and 3 more cleared (every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row), and the chain continues, and row 7 would end up with no open cell for its marker, which can't happen. So it can't go there.
14. Following that, that one can't be the marker: at D2 it would force F1 (the last open cell in region 2), then I3 (the last open cell in region 3), then A4, A5, C5, and 1 more cleared (together, two regions have open cells only in rows 4 and 5), and the chain continues, and region 7 would be left with no open cell for its marker.
15. First, 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.
16. Next, every remaining candidate in this region touches A4 and C4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
17. Then, that one can't be the marker: at G2 it would force E1 (the last open cell in region 2), then I3 (the last open cell in region 3), then H6 (the last open cell in region 7), and the chain continues, and row 5 would be left with no open cell for its marker.
18. After that, every open cell in row 2 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.
19. Now, if I2 were the marker, it would force G7, G8, G9, and 3 more cleared (together, two regions have open cells only in columns G and H), then A7, A8, C8, and 2 more cleared (every open cell in row 9 belongs to the same region, so that region's marker has to be somewhere in this row), then F8 (the last open cell in row 8), and row 7 would end up with no open cell for its marker, which can't happen. So it can't go there.
20. From there, place a marker at H2. Region has exactly one open cell left. Placing here clears the rest of row 2, column H, and its region. Placing here also clears its 1 touching neighbour.
21. Following that, 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.
22. First, 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.
23. Next, every open cell in row 9 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.
24. Then, place a marker at F8. Row 8 has exactly one open cell left. Placing here clears the rest of row 8, column F, and its region. Placing here also clears its 1 touching neighbour.
25. After that, place a marker at E1. Region has exactly one open cell left. Placing here clears the rest of row 1, column E, and its region.
26. Now, place a marker at I7. Row 7 has exactly one open cell left. Placing here clears the rest of row 7, column I, and its region.
27. From there, 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.
28. Following that, 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.
29. First, place a marker at B3. Region has exactly one open cell left. Placing here clears the rest of row 3, column B, and its region.
30. Next, place a marker at D5. Region has exactly one open cell left. Placing here clears the rest of row 5, column D, and its region. Placing here also clears its 1 touching neighbour.
31. Then, place a marker at A6. Region has exactly one open cell left. Placing here clears the rest of row 6, column A, and its region.
32. Finally, place a marker at C9. Region has exactly one open cell left.

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