Thanks Ed for correcting some typos.
Prelims
a) R3C78 = {49/58/67}, no 1,2,3
b) R45C9 = {59/68}
c) R56C1 = {29/38/47/56}, no 1
d) R7C23 = {18/27/36/45}, no 9
e) 19(3) cage at R3C4 = {289/379/469/478/568}, no 1
f) 10(3) cage at R4C2 = {127/136/145/235}, no 8,9
g) 21(3) cage at R4C5 = {489/579/678}, no 1,2,3
h) 21(3) cage at R5C7 = {489/579/678}, no 1,2,3
i) 11(3) cage at R7C1 = {128/137/146/236/245}, no 9
j) 19(3) cage at R8C2 = {289/379/469/478/568}, no 1
k) 19(3) cage at R8C8 = {289/379/469/478/568}, no 1
l) 11(4) cage at R1C5 = {1235}
m) 34(5) cage at R1C2 = {46789}
1. 45 rule on C1234 1 innie R9C4 = 5, placed for NR7C5
1a. 1 in C4 only in R678C4, locked for disjoint NR4C4, no 1 in R57C6 + R8C7
1b. 1 in R5 only in R5C23, locked for 10(3) cage at R4C2, no 1 in R4C2
2. 45 rule on C6789 1 innie R1C6 = 3
2a. Naked triple {125} in R123C5, locked for C5
2b. Naked triple {125} in R123C5, CPE no 1,2,5 in R3C67, clean-up: no 8 in R3C8
2c. R12C5 + R2C6 = {125} (hidden triple in NR1C4)
3. 3 in NR1C7 only in R23C9, locked for C9
3a. 13(3) cage at R1C9 = {139/238/346}, no 5,7
3b. 7 in C9 only in R6789C9, locked for NR6C6
4. 21(3) cage at R4C5 = {489/678}, 8 locked for C5
4a. 3 in C5 only in R789C5, locked for NR7C5
5. 45 rule on NR1C7 2 outies R26C8 = 15 = [69/78/96]
5a. Min R2C8 = 6 -> max R1C78 = 6, no 6,7,8,9 in R1C78
6. 7 in NR1C7 only in R5C78, locked for R5, clean-up: no 4 in R6C1
6a. 21(3) cage at R5C7 = {579/678}, no 4
6b. Hidden killer triple 1,2,4 in R1C78 + 13(3) cage at R1C9 for NR1C7, 13(3) cage (step 3a) contains one of 1,2,4 -> R1C78 = {124}
7. 45 rule on NR7C5 1 innie R8C8 = 1 outie R8C7 + 4, R8C8 = {6789}, R8C7 = {2345}
8. 1,2 in NR7C5 only in R8C6 + R9C678, locked for 20(5) cage at R8C6, clean-up: no 6 in R8C8 (step 7)
8a. 20(5) cage = {12368/12458/12467} (cannot be {12359} because 3,5 only in R8C7), no 9
8b. R26C8 = 15 (step 5) -> min R268C8 = 22, must contain 9, locked for C8, clean-up: no 4 in R3C7
9. 19(3) cage at R8C8 = {289/469/478} (cannot be {568} which clashes with R45C9), no 5
10. 45 rule on R12 3 outies R3C569 = 12
10a. Min R3C56 = 5 -> no 8,9 in R3C9
11. 45 rule on R6789 3 innies R6C158 = 1 outie R5C6 + 19
11a. Max R6C158 = 24 -> max R5C6 = 5
11b. Min R5C6 = 2 -> min R6C158 = 21, no 2,3 in R6C1, clean-up: no 8,9 in R5C1
12. 45 rule on R123 2 outies R4C13 = 1 innie R3C4
12a. Min R4C13 = 3 -> min R3C4 = 3
12b. Max R4C13 = 9, no 9 in R4C13
13. 45 rule on R789 1 innie R7C6 = 2 outies R6C79 + 2
13a. Min R6C79 = 3 -> min R7C6 = 5
13b. Max R6C79 = 7, no 7,8,9 in R6C79
14. 2 in C4 only in R45678C4, locked for disjoint NR4C4, no 2 in R5C6
14a. R6C158 = R5C6 + 19 (step 11)
14b. R5C6 = {45} -> R6C158 = 23,24 = {689/789}, no 4,5, 8,9 locked for R6, clean-up: no 6 in R5C1
14c. 13(3) cage at R6C2 = {157/247/256/346}
14d. Killer pair 6,7 in R6C158 and 13(3) cage, locked for R6
15. 15(3) cage at R5C6 = {159/249/258/456} (cannot be {168/267} because R5C6 only contains 4,5), no 7
15a. Max R56C6 = 9 -> min R7C6 = 6
16. 13(3) cage at R1C9 (step 3a) = {139/238/346}, R45C9 = {59/68} -> 13(3) cage + R45C9 must contain 9, locked for C9 and NR1C7
17. 3 in NR6C6 only in 22(5) cage at R6C7 = {12379/13459/13468/13567} (cannot be {23458/23467} which clash with 19(3) cage at R8C9), 1 locked for NR6C6
18. 45 rule on NR6C6 2 innies R6C68 = 1 outie R8C8 + 4, IOU no 4 in R6C6
19. Hidden killer triple 2,5,8 in R6C6, 22(5) cage at R6C7, R6C8 and 19(3) cage at R8C8 for NR6C6, R6C6 = {25}, 22(5) cage contains one of 2,5,8 -> 19(3) cage cannot contain more than one of 2,8 in R89C9
19a. 19(3) cage at R8C8 (step 9) = {469/478} (cannot be {289} which contains both of 2,8 in R89C9), no 2, 4 locked for C9 and NR6C6
19b. 13(3) cage at R1C9 (step 3a) = {139/238}, no 6
20. 4 in NR1C7 only in R1C78, locked for R1
20a. R1C78 = {14/24} -> R2C8 = {67}, clean-up: no 6 in R6C8 (step 5)
20b. 21(3) cage at R5C7 (step 6a) = {579/678}
20c. R6C8 = {89} -> no 8 in R5C78
20d. 34(5) cage at R1C2 = {46789}, 4 locked for R2 and NR1C4
21. 8 in NR1C7 only in R1245C9, locked for C9
21a. 19(3) cage at R8C8 (step 9) = {469/478}
21b. 8,9 only in R8C8 -> R8C8 = {89}, clean-up: no 3 in R8C7 (step 7)
[This elimination could have been obtained a bit earlier using Law of Leftovers for C6789, but I’m avoiding using it for this puzzle which has a fairly low SS score.]
21c. Naked pair {89} in R68C8, locked for C8
22. 22(5) cage at R6C7 (step 17) = {12379} (only remaining combination, cannot be {13567} which clashes with R89C9) -> R7C9 = 7, R7C7 = 9, R6C8 = 8, R2C8 = 7 (step 5), placed for NR2C7, R8C8 = 9, clean-up: no 6 in R3C7, no 4 in R3C8, no 3 in R5C1, no 2 in R7C23
22a. R6C6 = 5 (hidden single in NR6C6), R5C6 = 4, R7C6 = 6 (cage sum), both placed for disjoint nonet at R4C4, R8C7 = 5, clean-up: no 7 in R6C1, no 3 in R7C23
23. R6C158 = R5C6 + 19 (step 11)
23a. R5C6 = 4 -> R6C158 = 23 = {689} -> R6C5 = 9, placed for NR4C4, R6C1 = 6, placed for NR2C1, R5C1 = 5, R5C78 = [76], R5C5 = 8, placed for NR2C7, R4C5 = 4 (cage sum), R5C9 = 9, R4C9 = 5, R3C7 = 8, placed for NR1C4, R3C8 = 5, R7C5 = 3
24. 13(3) cage at R1C9 (step 3a) = {238} (only remaining combination), locked for C9 and NR1C7 -> R6C9 = 1, R7C8 = 2, R6C7 = 3
24a. Naked pair {14} in R1C78, locked for R1
25. R7C23 = {45} (only remaining combination, cannot be {18} which clashes with R7C4), locked for R7
25a. Naked pair {45} in R7C23, CPE no 4 in R8C2
26. 19(3) cage at R3C4 = {289/379} (cannot be {469/478} because R5C4 only contains 2,3) -> R3C4 = 9, placed for NR3C3, R4C4 = {78}
26a. R3C6 = 7, placed for NR1C4, R2C67 = 8 = [26], 2 placed for NR1C4, R12C5 = [51] , R1C4 = 6, R2C34 = [94]
27. R3C5 = 2, placed for NR2C7, 13(3) cage at R4C6 = [913]
28. R2C2 = 5 (hidden single in R2), R12C1 = 12 = [93], 3 placed for NR2C1, R7C23 = [45]
28a. 11(3) cage at R7C1 = {128} (only remaining combination), locked for C1 and NR2C1 -> R45C1 = [47], 7 placed for NR2C1, R9C2 = 9, R4C4 = 8, R5C4 = 2 (cage sum)
29. R6C4 = 7, R78C4 = [13], R8C3 = 8 (cage sum)
and the rest is naked singles, without using the nonets.