How to solve this 6×6 logic puzzle

6×6 · sharp · 14 steps

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This 6×6 board rates as sharp (difficulty score 960). Solving it from scratch takes 21 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.

First, 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.
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.
Then, 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.
After that, place a marker at D5. Region has exactly one open cell left. Placing here clears the rest of row 5, column D, and its region. Placing here also clears its 2 touching neighbours.
Now, every remaining candidate in this region touches E2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
From there, 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.
Following that, every remaining candidate in this region touches C3 and A4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
First, place a marker at A6. Region has exactly one open cell left. Placing here clears the rest of row 6, column A, and its region.
Next, together, two regions have open cells only in rows 3 and 4; 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.
Then, that one can't be the marker: at C1 it would force F2 (the last open cell in region 3), and column E would be left with no open cell for its marker.
After that, place a marker at C2. Region has exactly one open cell left. Placing here clears the rest of row 2, column C, and its region. Placing here also clears its 1 touching neighbour.
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.
From there, place a marker at E3. Region has exactly one open cell left. Placing here clears the rest of row 3, column E, and its region.
Finally, place a marker at F1. Region has exactly one open cell left.

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