Thanks Jean-Christophe. A fun puzzle!
Although I used the same key moves as the others, I missed one early move - Afmob's step 2c, step 1 in Mike's optimised walkthrough - only seeing my step 8 instead. That led to some significant differences in my solving path including a couple of fun steps later.
Missing that early step didn't seem to make the solution path any harder so I'll also rate this puzzle 1.25.
Here is my walkthrough.
Thanks Afmob for pointing out that my original step 19 was flawed. I've deleted it, renumbered the next 4 steps and inserted a new step 23; step 21 has been edited for clarity and step 22 is now shorter. There is also simplification of the mop-up stage. I've inserted a clean-up in step 28 that I'd originally omitted. That removed the last 5 steps!
Prelims
a) R34C2 = {49/58/67}, no 1,2,3
b) R34C3 = {17/26/35}, no 4,8,9
c) R3C78 = {16/25/34}, no 7,8,9
d) R67C7 = {13}, locked for C7, clean-up: no 4,6 in R3C8
e) R67C8 = {39/48/57}, no 1,2,6
f) R7C23 = {49/58/67}, no 1,2,3
g) R234C9 = {389/479/569/578}, no 1,2
h) 10(3) cage at R3C4 = {127/136/145/235}, no 8,9
i) 22(3) cage at R3C6 = {589/679}
j) R456C5 = {127/136/145/235}, no 8,9
k) R6789C9 = {1238/1247/1256/1346/2345}, no 9
l) 18(5) cage at R5C1 = {12348/12357/12456}, no 9
m) 32(5) cage at R4C8 = {26789/35789/45689}, no 1
1. 45 rule on C1 2 innies R59C1 = 9 = {18/27/36/45}, no 9 in R9C1
2. 45 rule on C9 2 innies R15C9 = 11 = {29/38/47/56}, no 1 in R1C9
2a. 1 in N3 locked in R123C8, locked for C8
2b. 1 in N6 locked in R6C79, locked for R6
3. 45 rule on R1234 2 innies R4C58 = 7 = [16/25/34/43/52], no 7,8,9, no 6 in R4C5
4. 32(5) cage at R4C8 = {26789/35789/45689}, 8 locked in R5C6789 for R5
5. 45 rule on R6789 2 innies R6C25 = 8 = {26/35}
6. 18(5) cage at R5C1 = {12357/12456}, 1 locked in R5C1234 for R5
7. R456C5 = {127/136/145/235}
7a. 1 of {145} must be in R4C5 -> no 4 in R4C5, clean-up: no 3 in R4C8 (step 3)
8. 45 rule on N3 1 innie R1C7 = 1 outie R4C9 + 3, R1C7 = {6789}, R4C9 = {3456}
8a. R234C9 = {389/479/569/578}
8b. 3,4 of {389/479} must be in R4C9 -> no 3,4 in R23C9
9. 45 rule on N7 1 outies R6C1 = 1 innie R9C3 + 5, R6C1 = {6789}, R9C3 = {1234}
10. 45 rule on R89 3 innies R8C19 + R9C9 = 8, no 6,7,8,9 in R8C1, no 7,8 in R89C9
11. 45 rule on C6789 3 outies R279C5 = 24 = {789}, locked for C5
12. 21(4) cage at R1C6 = {1389/1479/1569/1578/2379/2469/2478/2568/3459/3468/3567}, R1C7 + R2C5 = {6789} -> no 6,7,8,9 in R12C6
13. 23(4) cage at R8C4 = {3569/4568} (cannot be {1589/1679/2489/2579/2678/3479/3578} which clash with R79C5), no 1,2,7, 5,6 locked for N8, clean-up: no 6,7 in R6C1 (step 9)
13a. R9C3 = {34} -> no 3,4 in R8C45 + R9C4
14. Killer triple 7,8,9 in R79C5 + R89C4, locked for N8
14a. 7 in N8 locked in R79C5, locked for C5
15. Naked quint {12345} in R12789C6, locked for C6
15a. 22(3) cage at R3C6 = {589/679}
15b. 5 of {589} must be in R4C7 -> no 8 in R4C7
16. 5 in C6 locked in R12C6, locked for N2
16a. 21(4) cage at R1C6 (step 12) = {1569/1578/2568} (cannot be {3459} because 3,4,5 only in R12C6, cannot be {3567} because R2C5 only contains 8,9), no 3,4
16b. R2C5 = {89} -> no 8,9 in R1C7, clean-up: no 5,6 in R4C9 (step 8)
17. 3,4 in C6 locked in R789C6, locked for N8
18. R1C7 + R4C9 (step8) = [63/74]
18a. R234C9 (step 8a) = {389} (cannot be {479} which clashes with R1C7 + R4C9, cannot be {569/578} because R4C9 only contains 3,4) -> R4C9 = 3, R1C7 = 6 (step 8), R67C7 = [13], clean-up: no 5 in R3C3, no 1 in R3C8 , no 9 in R67C8, no 8 in R15C9, no 5 in R5C9 (both step 2), no 4 in R4C8 (step 3)
18b. Naked pair {89} in R23C9, locked for C9 and N3, clean-up: no 2 in R15C9 (step 2)
18c. Naked pair {89} in R2C59, locked for R2
19. 3 in C6 locked in R89C6
19a. 22(4) cage at R8C6 = {2389/3478}, no 1,5
19b. 2,3,4 must be in R89C6 -> no 2,4 in R8C7
20. R6C1 + R9C3 (step 9) = [83/94]
20a. R678C1 = {189/279/369/378/468} (cannot be {459} which clashes with R6C1 + R9C3, cannot be {567} because R6C1 only contains 8,9), no 5
20b. 1,2,4 of {189/279/468} must be in R8C1 -> no 1,2,4 in R7C1
21. 23(4) cage at R1C4 = {1679/2579/2678/3479/3569/3578/4568} (cannot be {1589/2489}
which clash with R2C5)
21a. 8,9 only in R1C4 -> R1C4 = {89}
21b. 1,2 of {1679/2579/2678} must be in R1C5 -> no 1,2 in R2C34
22. Naked pair {89} in R1C4 and R2C5, locked for N2
23. R3C6 = {67} -> 22(3) cage at R3C6 = {679} (only remaining combination), no 5,8, 6 locked in R34C6, locked for C6, 9 locked in R4C67, locked for R4, clean-up: no 4 in R3C2
24. 8 in R4 locked in R4C12, locked for N4 -> R6C1 = 9, R9C3 = 4 (step 9), clean-up: no 9 in R7C23
25. R7C5 = 9 (hidden single in R7), R2C5 = 8, R9C5 = 7, R1C4 = 9, R23C9 = [98], R3C2 = 9 (hidden single in R3), R4C2 = 4
25a. R7C5 = 9 -> R67C6 = 8 = [71],
R34C6 = [69], R4C7 = 7, R5C6 = 8, R7C4 = 2, R89C6 = [43], R8C7 = 8 (step
19a), clean-up:
no 4 in R1C9 (step 2), no 1 in R3C3, no 2 in R4C3, no 4 in R6C8, no 5 in R7C8
26. R6C8 = 8 (hidden single in R6), R7C8 = 4
27. R4C1 = 8 (hidden single in R4), clean-up: no 1 in R8C1 (step
20a)
27a. 4 in C1 locked in R123C1 -> R123C1 = 10 = {145}, locked for C1 and N1
28. R7C4 = 2 -> R6C34 = 10 = [64], clean-up:
no 2 in R6C25 (step 5), no 2 in R3C3, no 7 in R7C2
29. R8C3 = 9 (hidden single in C3)
29a. 1 in N7 locked in 19(4) cage = {1279/1369}, no 5,8
29b. 3 of {1369} must be in R8C2 -> no 6 in R8C2 (added for completeness)
30. R7C23 = {58} (hidden pair in N7), locked for R7
31. R5C9 = 4 (hidden single in C9), R1C9 = 7 (step 2), R7C9 = 6, R7C1 = 7, R8C1 = 2 (step
20a), R59C1 = [36], R89C2 = [31],
R6C25 = [53], R689C9 = [215], R8C8 = 7, R7C23 = [85], R9C4 = 8, R4C3 = 1, R3C3 = 7, R2C34 = [37], R12C2 = [26], R1C3 = 8, R5C23 = [72], R12C6 = [52]
32. 10(3) cage at R3C4 = {136/145}
32a. 1 locked in R3C45, locked for R3 and N2
-> R1C5 = 4, R1C1 = 1, R1C8 = 3, clean-up: no 4 in R3C7
32b. R3C45 = {13} -> R4C4 = 6 (step 32)
and the rest is naked singles
1 2 8 9 4 5 6 3 7
5 6 3 7 8 2 4 1 9
4 9 7 3 1 6 5 2 8
8 4 1 6 2 9 7 5 3
3 7 2 1 5 8 9 6 4
9 5 6 4 3 7 1 8 2
7 8 5 2 9 1 3 4 6
2 3 9 5 6 4 8 7 1
6 1 4 8 7 3 2 9 5