An Expert 10×10 Puzzle Solved with Forced Chain in 31 Steps

This 10×10 board rates as expert (difficulty score 1505). Solving it from scratch takes 31 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 column D, so its marker has to land there; that clears every other open cell in the column.
2. Next, every remaining candidate in this region touches I2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
3. Then, every remaining candidate in this region touches G5, 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 C5 and E5, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
5. Now, marking A1 would force J2 (the last open cell in region 4), then D4, F4 and G4 cleared (together, two regions have open cells only in rows 3 and 4), then F5 (the last open cell in region 6), and the chain continues, and then region 7 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 J2 (the last open cell in region 4), then A6, A7, A8, and 2 more cleared (every open cell left in this region sits in column A, so its marker has to land there), then C10 (the last open cell in region 10), and region 7 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 J2 (the last open cell in region 4), then A8, A9, A10, and 4 more cleared (together, two regions have open cells only in columns A and B), and region 10 would be left with no open cell for its marker.
8. First, that one can't be the marker: at F1 it would force J2 (the last open cell in region 4), then G4 (the last open cell in region 6), then E3 (the last open cell in region 3), and the chain continues, and region 7 would be left with no open cell for its marker.
9. Next, marking G1 would force J2 (the last open cell in region 4), then F6, F7, F8, and 2 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then C8, H8, C9, and 4 more cleared (every open cell in column E belongs to the same region, so that region's marker has to be somewhere in this column), and the chain continues, and then column I 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 J2 (the last open cell in region 4), then I9 and I10 cleared (every open cell left in this region sits in column I, so its marker has to land there), then F6, G6, F7, and 9 more cleared (every open cell in column E belongs to the same region, so that region's marker has to be somewhere in this column), 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.
11. After that, that one can't be the marker: at A2 it would force E1 cleared (every open cell left in this region sits in row 1, so its marker has to land there), then C6, C7, C8, and 2 more cleared (every open cell left in this region sits in column C, so its marker has to land there), then B7, B8, B9, and 1 more cleared (every open cell left in this region sits in column B, so its marker has to land there), and region 10 would be left with no open cell for its marker.
12. Now, marking B2 would force A6, A7, A8, and 2 more cleared (every open cell left in this region sits in column A, so its marker has to land there), then C10 (the last open cell in region 10), and then region 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 A8, A9, A10, and 4 more cleared (together, two regions have open cells only in columns A and B), and region 10 would end up with no open cell for its marker, which can't happen. So it can't go there.
14. Following that, marking E2 would force B4 cleared (every remaining candidate in this region touches B4), then A6, A7, A8, and 2 more cleared (every open cell left in this region sits in column A, so its marker has to land there), then B7, B8, B9, and 4 more cleared (together, two regions have open cells only in columns B and C), and then region 10 would be left with no open cell for its marker. So E2 can't be the marker there.
15. First, if F2 were the marker, it would force G4 (the last open cell in region 6), then A3 cleared (every open cell left in this region sits in row 3, so its marker has to land there), then A5 (the last open cell in region 1), 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.
16. Next, that one can't be the marker: at I1 it would force G2 (the last open cell in row 2), then F6, F7, F8, and 2 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then C8, H8, C9, and 3 more cleared (every open cell in column E belongs to the same region, so that region's marker has to be somewhere in this column), and the chain continues, and column J would be left with no open cell for its marker.
17. Then, every open cell left in this region sits in column J, so its marker has to land there; that clears every other open cell in the column.
18. After that, marking J1 would force E3, F3, G3, and 5 more cleared (every open cell in row 2 belongs to the same region, so that region's marker has to be somewhere in this row), then F6, G6, F7, and 14 more cleared (every open cell in column E belongs to the same region, so that region's marker has to be somewhere in this column), then G4 cleared (every open cell in column F belongs to the same region, so that region's marker has to be somewhere in this column), and the chain continues, and then column I would be left with no open cell for its marker. So J1 can't be the marker there.
19. Now, 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.
20. From there, place a marker at E1. Row 1 has exactly one open cell left. Placing here clears the rest of row 1, column E, and its region.
21. Following that, if A3 were the marker, it would force D4, F4 and G4 cleared (every open cell left in this region sits in row 4, so its marker has to land there), then F5 (the last open cell in region 6), then D6 (the last open cell in region 5), and region 7 would end up with no open cell for its marker, which can't happen. So it can't go there.
22. First, 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.
23. Next, together, two regions have open cells only in rows 4 and 5; 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.
24. Then, place a marker at D6. Region has exactly one open cell left. Placing here clears the rest of row 6, column D, and its region. Placing here also clears its 1 touching neighbour.
25. After that, 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. Placing here also clears its 1 touching neighbour.
26. Now, place a marker at B4. Region has exactly one open cell left. Placing here clears the rest of row 4, column B, and its region.
27. From there, 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.
28. Following that, place a marker at I8. Region has exactly one open cell left. Placing here clears the rest of row 8, column I, and its region. Placing here also clears its 1 touching neighbour.
29. First, place a marker at C10. Region has exactly one open cell left. Placing here clears the rest of row 10, column C, and its region.
30. Next, 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.
31. Finally, place a marker at H3. Region has exactly one open cell left.

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