An Expert 10×10 Puzzle Solved with Forced Chain in 28 Steps

This 10×10 board rates as expert (difficulty score 1307). Solving it from scratch takes 28 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, together, two regions have open cells only in rows 9 and 10; 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.
2. Next, every open cell left in this region sits in column A, so its marker has to land there; that clears every other open cell in the column.
3. Then, together, two regions have open cells only in rows 7 and 8; 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.
4. After that, every open cell left in this region sits in row 6, so its marker has to land there; that clears every other open cell in the row.
5. Now, together, two regions have open cells only in columns B and C; 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.
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, if E1 were the marker, it would force B2 (the last open cell in region 1), then G3 (the last open cell in region 3), then D5 (the last open cell in region 4), and row 6 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 F1 it would force B2 (the last open cell in region 1), then G3 (the last open cell in region 3), then D5 (the last open cell in region 4), and row 6 would be left with no open cell for its marker.
9. Next, marking G1 would force B2 (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.
10. Then, if H1 were the marker, it would force B2 (the last open cell in region 1), then G3 (the last open cell in region 3), then D5 (the last open cell in region 4), and row 6 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 I1 it would force B2 (the last open cell in region 1), then C6 (the last open cell in region 6), then D3 (the last open cell in region 4), and region 2 would be left with no open cell for its marker.
12. Now, marking J1 would force B2 (the last open cell in region 1), then C6 (the last open cell in region 6), then D3 (the last open cell in region 4), and then region 2 would be left with no open cell for its marker. So J1 can't be the marker there.
13. From there, 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.
14. Following that, marking E2 would force D5 (the last open cell in region 4), then G3 (the last open cell in region 3), then B6 (the last open cell in region 6), and the chain continues, and then row 9 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, region 3 would end up with no open cell for its marker, which can't happen. So it can't go there.
16. Next, every remaining candidate in this region touches F4, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
17. Then, that one can't be the marker: at C1 it would force B6 (the last open cell in region 6), then A8 (the last open cell in region 7), then J7 (the last open cell in region 8), and the chain continues, and column G would be left with no open cell for its marker.
18. After that, place a marker at B1. Region has exactly one open cell left. Placing here clears the rest of row 1, column B, and its region.
19. Now, place a marker at C6. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
20. From there, every open cell in row 5 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.
21. Following that, place a marker at E4. Row 4 has exactly one open cell left. Placing here clears the rest of row 4, column E, and its region. Placing here also clears its 2 touching neighbours.
22. First, place a marker at D2. Region has exactly one open cell left. Placing here clears the rest of row 2, column D, and its region.
23. Next, place a marker at G3. Region has exactly one open cell left. Placing here clears the rest of row 3, column G, and its region.
24. Then, place a marker at F10. Region has exactly one open cell left. Placing here clears the rest of row 10, column F, and its region.
25. 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. Placing here also clears its 1 touching neighbour.
26. Now, place a marker at H8. Region has exactly one open cell left. Placing here clears the rest of row 8, column H, and its region.
27. From there, place a marker at I5. Region has exactly one open cell left.
28. Finally, place a marker at A7. Region has exactly one open cell left.

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