An Expert 8×8 Puzzle Solved with Forced Chain in 20 Steps

This 8×8 board rates as expert (difficulty score 1181). Solving it from scratch takes 20 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, place a marker at B8. Region has exactly one open cell left. Placing here clears the rest of row 8, column B, and its region. Placing here also clears its 2 touching neighbours.
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, every remaining candidate in this region touches D2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
4. After that, that one can't be the marker: at C1 it would force H5, H6 and H7 cleared (every open cell left in this region sits in column H, so its marker has to land there), then G2, G3 and G6 cleared (every open cell left in this region sits in column G, so its marker has to land there), then E6 and E7 cleared (every remaining candidate in this region touches E6 and E7), and the chain continues, and row 3 would be left with no open cell for its marker.
5. Now, marking D1 would force H5, H6 and H7 cleared (every open cell left in this region sits in column H, so its marker has to land there), then G2, G3 and G6 cleared (every open cell left in this region sits in column G, so its marker has to land there), then F2, F3, F4, and 1 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 row 3 would be left with no open cell for its marker. So D1 can't be the marker there.
6. From there, that one can't be the marker: at F1 it would force C2 (the last open cell in row 2), then E3 (the last open cell in region 1), and region 4 would be left with no open cell for its marker.
7. Following that, together, two regions have open cells only in columns G and H; 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 E6 and E7, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
9. Next, if C2 were the marker, it would force D7 (the last open cell in column D), then E4 and E5 cleared (every open cell left in this region sits in column E, so its marker has to land there), then G4 cleared (every remaining candidate in this region touches G4), 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.
10. Then, marking G1 would force E2 (the last open cell in row 2), and then row 3 would be left with no open cell for its marker. So G1 can't be the marker there.
11. After that, every open cell left in this region sits in column H, so its marker has to land there; that clears every other open cell in the column.
12. Now, marking E2 would force H1 (the last open cell in row 1), and then row 3 would be left with no open cell for its marker. So E2 can't be the marker there.
13. From there, if H1 were the marker, it would force F2 (the last open cell in row 2), and column E would end up with no open cell for its marker, which can't happen. So it can't go there.
14. Following that, 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. Placing here also clears its 1 touching neighbour.
15. First, place a marker at H2. Row 2 has exactly one open cell left. Placing here clears the rest of row 2, column H, and its region.
16. Next, place a marker at F3. Row 3 has exactly one open cell left. Placing here clears the rest of row 3, column F, and its region. Placing here also clears its 1 touching neighbour.
17. Then, place a marker at D7. Region has exactly one open cell left. Placing here clears the rest of row 7, column D, and its region. Placing here also clears its 1 touching neighbour.
18. After that, place a marker at G5. Region has exactly one open cell left. Placing here clears the rest of row 5, column G, and its region.
19. Now, place a marker at C4. Region has exactly one open cell left.
20. Finally, place a marker at A6. Region has exactly one open cell left.

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