An Expert 7×7 Puzzle Solved with Forced Chain in 33 Steps

This 7×7 board rates as expert (difficulty score 1561). Solving it from scratch takes 33 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 remaining candidate in this region touches F2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
2. Next, that one can't be the marker: at C1 it would force G2 (the last open cell in region 2), then F6 and F7 cleared (every open cell left in this region sits in column F, so its marker has to land there), then D3, D5 and D6 cleared (together, two regions have open cells only in columns E and D), and the chain continues, and column F would be left with no open cell for its marker.
3. Then, marking D1 would force G2 (the last open cell in region 2), then F6 and F7 cleared (every open cell left in this region sits in column F, so its marker has to land there), then E3, E4 and E5 cleared (every open cell left in this region sits in column E, so its marker has to land there), and the chain continues, and then row 3 would be left with no open cell for its marker. So D1 can't be the marker there.
4. After that, every remaining candidate in this region touches B2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
5. Now, if C2 were the marker, it would force A7 cleared (every open cell left in this region sits in column A, so its marker has to land there), then A1 cleared (every open cell left in this region sits in row 1, so its marker has to land there), then A3 (the last open cell in region 1), and the chain continues, and row 6 would end up with no open cell for its marker, which can't happen. So it can't go there.
6. From there, if E1 were the marker, it would force A2 (the last open cell in row 2), then B4, F4 and G4 cleared (every open cell left in this region sits in row 4, so its marker has to land there), then C3, D3, C5, and 1 more cleared (every remaining candidate in this region touches C3 and D3 and C5 and D5), and the chain continues, and region 6 would end up with no open cell for its marker, which can't happen. So it can't go there.
7. Following that, together, two regions have open cells only in columns F 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.
8. First, every remaining candidate in this region touches D6, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
9. Next, that one can't be the marker: at D2 it would force A1 and B1 cleared (every open cell left in this region sits in row 1, so its marker has to land there), then A3 (the last open cell in region 1), then E4 and E5 cleared (every open cell left in this region sits in column E, so its marker has to land there), and the chain continues, and row 6 would be left with no open cell for its marker.
10. Then, marking E2 would force G1 (the last open cell in region 2), then A3 (the last open cell in region 1), then D7 (the last open cell in region 7), and then row 6 would be left with no open cell for its marker. So E2 can't be the marker there.
11. After that, if A3 were the marker, it would force B6 (the last open cell in region 3), then D5 (the last open cell in region 6), and column C would end up with no open cell for its marker, which can't happen. So it can't go there.
12. Now, marking C3 would force E6 (the last open cell in row 6), and then column D would be left with no open cell for its marker. So C3 can't be the marker there.
13. From there, if B1 were the marker, it would force G2 (the last open cell in region 2), then E4 and E5 cleared (every remaining candidate in this region touches E4 and E5), then D3 cleared (every remaining candidate in this region touches D3), and the chain continues, and column C would end up with no open cell for its marker, which can't happen. So it can't go there.
14. Following that, 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.
15. First, if D3 were the marker, it would force E5 (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.
16. Next, 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.
17. Then, that one can't be the marker: at E3 it would force D7 (the last open cell in region 7), then C5 (the last open cell in region 6), and row 6 would be left with no open cell for its marker.
18. After that, every remaining candidate in this region touches D5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
19. Now, every open cell left in this region sits in column C, so its marker has to land there; that clears every other open cell in the column.
20. From there, every remaining candidate in this region touches B6, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
21. Following that, that one can't be the marker: at F1 it would force A2 (the last open cell in region 1), then B4 (the last open cell in region 3), then E5 (the last open cell in region 5), and the chain continues, and row 6 would be left with no open cell for its marker.
22. First, every open cell left in this region sits in column G, so its marker has to land there; that clears every other open cell in the column.
23. Next, every remaining candidate in this region touches E4, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
24. Then, marking G1 would force A2 (the last open cell in region 1), then B4 (the last open cell in region 3), then E5 (the last open cell in region 5), and the chain continues, and then row 6 would be left with no open cell for its marker. So G1 can't be the marker there.
25. After that, place a marker at G2. Region has exactly one open cell left. Placing here clears the rest of row 2, column G, and its region. Placing here also clears its 1 touching neighbour.
26. Now, place a marker at A1. Region has exactly one open cell left.
27. From there, place a marker at B3. Row 3 has exactly one open cell left. Placing here clears the rest of row 3, column B, and its region.
28. Following that, 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.
29. First, every remaining candidate in this region touches E5, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
30. Next, place a marker at D4. Region has exactly one open cell left. Placing here clears the rest of row 4, column D, and its region.
31. Then, place a marker at F5. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
32. After that, place a marker at E7. Region has exactly one open cell left. Placing here clears the rest of row 7, column E, and its region.
33. Finally, place a marker at C6. Region has exactly one open cell left.

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