An Expert 10×10 Puzzle Solved with Forced Chain in 34 Steps

This 10×10 board rates as expert (difficulty score 1566). Solving it from scratch takes 34 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 remaining candidate in this region touches G3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
2. Next, 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.
3. Then, marking A1 would force G2 (the last open cell in region 3), and then region 6 would be left with no open cell for its marker. So A1 can't be the marker there.
4. After that, if B1 were the marker, it would force G2 (the last open cell in region 3), and region 6 would end up with no open cell for its marker, which can't happen. So it can't go there.
5. Now, that one can't be the marker: at C1 it would force G2 (the last open cell in region 3), and region 6 would be left with no open cell for its marker.
6. From there, 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.
7. Following that, marking D1 would force G2 (the last open cell in region 3), and then region 6 would be left with no open cell for its marker. So D1 can't be the marker there.
8. First, every remaining candidate in this region touches C3 and E3, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
9. Next, if E1 were the marker, it would force G2 (the last open cell in region 3), and region 6 would end up with no open cell for its marker, which can't happen. So it can't go there.
10. Then, 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.
11. After that, if H1 were the marker, it would force J2 (the last open cell in region 6), then A3, B3, A4, and 4 more cleared (together, two regions have open cells only in rows 3 and 4), then I9, G4, G5, and 2 more cleared (together, two regions have open cells only in columns I and G), and the chain continues, and row 4 would end up with no open cell for its marker, which can't happen. So it can't go there.
12. Now, that one can't be the marker: at I1 it would force H3 (the last open cell in region 6), then F5, F6, F7, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then A2, B2, C2, and 6 more cleared (together, two regions have open cells only in rows 2 and 4), and the chain continues, and row 4 would be left with no open cell for its marker.
13. From there, that one can't be the marker: at A2 it would force H3 (the last open cell in region 6), then D4 (the last open cell in region 1), and region 5 would be left with no open cell for its marker.
14. Following that, marking B2 would force H3 (the last open cell in region 6), then D4 (the last open cell in region 1), and then region 5 would be left with no open cell for its marker. So B2 can't be the marker there.
15. First, if C2 were the marker, it would force H3 (the last open cell in region 6), then D4 (the last open cell in region 1), and region 5 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 D2 it would force H3 (the last open cell in region 6), then F4 (the last open cell in region 5), and region 2 would be left with no open cell for its marker.
17. Then, every remaining candidate in this region touches C4 and E4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
18. After that, marking G1 would force F5, F6, F7, and 3 more cleared (every open cell left in this region sits in column F, so its marker has to land there), then E6, E7, E8, and 2 more cleared (every open cell left in this region sits in column E, so its marker has to land there), then A3, B3, H3, and 6 more cleared (together, two regions have open cells only in rows 3 and 4), and the chain continues, and then row 4 would be left with no open cell for its marker. So G1 can't be the marker there.
19. Now, marking E2 would force J1 (the last open cell in region 3), then H3 (the last open cell in region 6), then D4 (the last open cell in region 1), and then region 5 would be left with no open cell for its marker. So E2 can't be the marker there.
20. From there, marking J1 would force H4, H5, H6, and 4 more cleared (every open cell left in this region sits in column H, so its marker has to land there), then I9, G4, G5, and 2 more cleared (together, two regions have open cells only in columns I and G), then F5, F6, F7, and 3 more cleared (every open cell left in this region sits in column F, 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.
21. Following that, 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.
22. First, 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 2 touching neighbours.
23. Next, place a marker at D3. Region has exactly one open cell left. Placing here clears the rest of row 3, column D, and its region.
24. Then, place a marker at E5. Region has exactly one open cell left. Placing here clears the rest of row 5, column E, and its region.
25. 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 1 touching neighbour.
26. Now, 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. Placing here also clears its 1 touching neighbour.
27. From there, together, two regions have open cells only in columns I and J; 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.
28. Following that, every remaining candidate in this region touches A9, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
29. First, every open cell left in this region sits in row 10, so its marker has to land there; that clears every other open cell in the row.
30. Next, every remaining candidate in this region touches B9, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
31. Then, 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.
32. After that, place a marker at J9. Region has exactly one open cell left. Placing here clears the rest of row 9, column J, and its region.
33. Now, place a marker at I2. Region has exactly one open cell left.
34. 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. ∎