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There are twelve inner windows, each overlapping with at least one other; there are four different windows overlapping at R5C5. I’ve identified each window by the corner furthest from R5C5, for example window at R1C9 as WR1C9.

Prelims

a) 24(3) cage at R2C4 = {789}
b) 10(3) cage at R2C7 = {127/136/145/235}, no 8,9
c) 6(3) cage at R4C2 = {123}
d) 7(3) cage at R4C8 = {124}
e) 23(3) cage at R8C4 = {689}

Steps resulting from Prelims
1a. Naked triple {789} in 24(3) cage at R2C4, locked for R2, N2, WR2C2 and WR2C8
1b. Naked triple {123} in 6(3) cage at R4C2, locked for C2, N4, WR2C2 and WR8C2
1c. Naked triple {124} in 7(3) cage at R4C8, locked for C8, N6, WR2C8 and WR8C8
1d. Naked triple {689} in 23(3) cage at R8C4, locked for R8, N8, WR8C2 and WR8C8
[And resulting from these …]
1e. Naked triple {456} in R2C23 + R3C2, locked for N1
1f. Naked triple {356} in R2C78 + R3C8, locked for N3
1g. Naked triple {457} in R7C2 + R8C23, locked for N7
1h. Naked triple {357} in R7C8 + R8C78, locked for N9

2. R2C19 = {12} (hidden pair in R2)
2a. 4 in R2 only in R2C23, locked for N1
2b. 3 in R2 only in R2C78, locked for N3
2c. Naked pair {56} in R3C28, locked for R3

3. R8C19 = {12} (hidden pair in R8)
3a. Naked pair {12} in R28C1, locked for C1
3b. Naked pair {12} in R28C9, locked for C9

4. 18(3) cage at R1C1 = {189/279} (cannot be {378} because R2C1 only contains 1,2), 9 locked for C1 and N1
4a. Killer triple 7,8,9 in 18(3) cage and R1C2, locked for N1
4b. 3 in N1 only in R13C3, locked for C3

5. R9C2 = 9 (hidden single in C2), R1C2 = 8 (hidden single in C2)
5a. 18(3) cage at R1C1 (step 4) = {279} (only remaining combination) -> R2C1 = 2, R13C1 = {79}, locked for C1
5b. R8C19 = [12]

6. R2C9 = 1 -> R2C78 = 9 = {36}, locked for R2 and N3 -> R3C8 = 5, R3C2 = 6

7. Naked pair {37} in R78C8, locked for C8 and N9 -> R1C8 = 9, R13C1 = [79], R1C9 = 4, R1C7 = 2, R2C78 = [36], R8C7 = 5, R9C8 = 8, R9C9 = 6, R7C9 = 9, R9C1 = 3, R9C3 = 2

8. Naked pair {47} in R8C23, locked for R8 and N7 -> R7C2 = 5, R2C23 = [45], R8C23 = [74], R78C8 = [73]

9. 3 in WR1C1 only in R1C345, locked for R1
9a. 4 in WR1C1 only in R45C1, locked for C1
9b. 6 in WR1C9 only in R1C56, locked for R1
9c. 6 in WR9C1 only in R567C1, locked for C1
9d. 7 in WR9C1 only in R9C45, locked for R9
9e. 3 in WR9C9 only in R56C9, locked for C9
9f. 4 in WR9C9 only in R9C567, locked for R9
9g. 6 in WR1C1 only in R1C5 + R5C1, CPE no 6 in R5C5
9h. 3 in WR1C9 only in R1C5 + R5C9, CPE no 3 in R5C5
9i. 4 in WR9C1 only in R5C1 + R9C5, CPE no 4 in R5C5

10. 5 in WR3C3 only in R45C45, locked for N5
10a. 5 in WR7C3 only in R5C45, locked for R5 and N5
10b. 5 in R4 only in R4C19, CPE no 5 in R1C5 using WR1C1 and WR1C9
10c. 5 in R6 only in R6C19, CPE no 5 in R9C5 using WR9C1 and WR9C9
10d. R5C5 = 5 (hidden single in C5)

11. Hidden killer quad 1,2,3,4 in R5C4, 18(3) cage at R6C3 and R7C45 for WR7C3, 18(3) cage contains one of 1,2,3,4, R7C45 = {1234} -> R5C4 = {1234}
11a. Killer quad 1,2,3,4 in R3C345 + R5C4, locked for WR3C3

12. Killer quad 6,7,8,9 in R4C3457, locked for R4 -> R4C8 = 5, R1C6 = 6, R1C5 = 3, R1C34 = [15], R3C3 = 3, placed for WR3C3, R4C1 = 4, R5C1 = 6, R67C1 = [58], R7C3 = 6, placed for WR7C3, R9C45 = [74], R9C67 = [51], R7C7 = 4, placed for WR7C7
[It feels like the puzzle is cracked, but there’s still quite a lot of work to do using the windows.]

13. Naked pair {37} in R56C9, locked for C9 and N6 -> R3C9 = 8, R3C7 = 7, placed for WR3C7

14. Naked pair {12} in R37C5, locked for C5

15. 18(3) cage at R6C3 contains one of 1,2,3,4 -> R6C4 = {1234}

16. R3C6 = 4 (hidden single in C6)

17. Naked pair {12} in R3C45, locked for WR3C3 -> R5C4 = 4
17a. R6C8 = 4 (hidden single in C8)

18. R6C7 = 6 (hidden single in R6)

19. 7 in R4 only in R4C35, locked for WR3C3

20. R5C8 = 7 (hidden single in R5), R6C8 = 3
20a. Naked pair {12} in R6C24, locked for R6
20b. Naked pair {12} in R36C4, locked for C4 -> R7C4 = 3

21. 7 in WR7C3 only in R6C35, locked for R6
21a. Naked pair {89} in R68C6, locked for C6 -> R2C6 = 7

22. Naked pair {89} in R45C7, locked for WR3C7

23. Naked pair {12} in R7C56, locked for WR7C7 -> R5C6 = 3
23a. R4C2 = 3 (hidden single in C2)

24. Naked pair {89} in R5C7 + R6C6, locked for WR7C7 -> R6C5 = 7, R4C5 = 6
24a. R4C3 = 7 (hidden single in R4), R8C4 = 6 (hidden single in R8)

25. R6C5 = 7 -> R6C34 = 11 = [92]

and the rest is naked singles, without using the windows.

I'll rate my walkthrough at 1.25. This is based on steps 10c, 10d, 11 and 12; even though it felt like it was cracked after this, there was still quite a lot of work to do using the windows.