A Medium 10×10 Puzzle Solved with Shape Squeeze in 20 Steps

This 10×10 board rates as medium (difficulty score 850). Solving it from scratch takes 20 logical steps, using 6 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Shape squeeze. Every step below is forced: nothing here is a guess.

1. First, 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.
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, place a marker at B6. Region has exactly one open cell left. Placing here clears the rest of row 6, column B, and its region. Placing here also clears its 2 touching neighbours.
4. After that, 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.
5. Now, place a marker at E1. Region 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.
6. From there, every remaining candidate in this region touches G2 and G3, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
7. Following that, every open cell left in this region sits in row 4, so its marker has to land there; that clears every other open cell in the row.
8. First, every remaining candidate in this region touches C8 and C9, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
9. Next, place a marker at C10. Region has exactly one open cell left. Placing here clears the rest of row 10, column C, and its region. Placing here also clears its 1 touching neighbour.
10. Then, place a marker at D8. Region has exactly one open cell left. Placing here clears the rest of row 8, column D, and its region.
11. After that, place a marker at A9. Region has exactly one open cell left. Placing here clears the rest of row 9, column A, and its region.
12. Now, place a marker at F7. Region has exactly one open cell left. Placing here clears the rest of row 7, column F, and its region.
13. From there, 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.
14. Following that, every open cell left in this region sits in row 5, so its marker has to land there; that clears every other open cell in the row.
15. First, every open cell in column J belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
16. Next, every remaining candidate in this region touches H3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
17. Then, place a marker at H2. Region has exactly one open cell left. Placing here clears the rest of row 2, column H, and its region.
18. After that, place a marker at J3. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
19. Now, 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.
20. Finally, place a marker at I5. Region has exactly one open cell left.

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