Thanks Afmob for correcting typos and for pointing out when I reached naked singles without using the diagonals.
Prelims
a) R23C1 = {16/25/34}, no 7,8,9
b) R34C2 = {13}
c) R34C9 = {49/58/67}, no 1,2,3
d) R67C1 = {18/27/36/45}, no 9
e) R67C8 = {18/27/36/45}, no 9
f) R78C9 = {18/27/36/45}, no 9
g) R89C1 = {18/27/36/45}, no 9
h) R89C2 = {49/58/67}, no 1,2,3
i) 22(3) cage at R1C1 = {589/679}
j) 24(3) cage at R3C7 = {789}
k) 11(3) cage at R6C2 = {128/137/146/236/245}, no 9
l) 14(4) cage at R2C5 = {1238/1247/1256/1346/2345}, no 9
Steps resulting from Prelims
1a. 22(3) cage at R1C1 = {589/679}, 9 locked for N1
1b. Naked pair {13} in R34C2, locked for C2
2. 45 rule on C12 1 outie R7C3 = 1, placed for D/, clean-up: no 8 in R6C1, no 8 in R6C8, no 8 in R89C1, no 8 in R8C9
2a. R7C3 = 1 -> R67C2 = 10 = {28/46}, no 5,7
3. 45 rule on C89 1 outie R3C7 = 9, placed for D/, clean-up: no 4 in R4C9, no 4 in R9C2
3a. Naked pair {78} in R34C8, locked for C8, clean-up: no 1,2 in R6C8, no 2 in R7C8
4. 9 in N9 only in 12(3) cage at R8C8 = {129}, locked for N9, clean-up: no 7,8 in R7C9, no 7 in R8C9
4a. 7,8 in N9 only in R789C7, locked for C7
4b. 9 in R7 only in R7C456, locked for N8
4c. 17(3) cage at R8C6 = {278/368/458/467}, no 1
5. Hidden killer triple 7,8,9 in R4C8, R4C9 and 15(3) cage at R5C8 for N6, R4C8 = {78}, 15(3) cage cannot contain more than one of 7,8,9 -> R4C9 = {789}, clean-up: no 7,8 in R3C9
5a. 45 rule on R123 4 outies R4C2489 = 22 = [1489/1579]/[16]{78}/[3289]/[34]{78} -> R4C4 = {2456}
6. 37(7) cage at R4C5 must contain both of 8,9, CPE no 8,9 in R6C6
7. 9 on D\ only in 22(3) cage at R1C1 or 12(3) cage at R8C8, only one of them can have 9 on D\ -> there must be 9 in one of R1C2 + R9C8, CPE no 9 in R9C2, clean-up: no 4 in R8C2
7a. Killer pair 6,8 in R67C2 and R89C2, locked for C2
7b. 22(3) cage = {589/679} -> R1C1 = {68}
7c. Hidden killer pair 2,4 in R5C2 and R67C2 for C2, R67C2 contains one of 2,4 -> R5C2 = {24}
8. 9 in C1 only in R45C1, locked for N4
8a. R5C2 = {24} -> 16(3) cage at R4C1 = {259/349} -> R45C1 = {39/59}
8b. 37(7) cage at R4C5 must contain 9 in R46C5, locked for C5 and N5
9. 1 in C1 only in R23C1 = {16} or R67C1 = [18] -> no 6 in R67C1 (locking-out cages), no 3 in R67C1
9a. Locking-cages killer pair 6,8 in R1C1, R23C1 and R67C1 for C1, no 6 in R89C1, clean-up: no 3 in R89C1
9a. 6 in C1 only in R123C1, locked for N1
9b. Killer pair 5,7 in R89C1 and R89C2, locked for N7, clean-up: no 2,4 in R6C1
10. R89C3 = {39} (hidden pair in N7), locked for C3 and 17(4) cage at R8C3
10a. R89C3 = 12 -> R9C45 = 5 = {14}, locked for R9 and N8, clean-up: no 5 in R8C1
10b. Naked pair {29} in R9C89, locked for R9 and N9 -> R89C3 = [93], clean-up: no 7 in R8C1
10c. R8C8 = 1, placed for D\
10d. 17(3) cage at R8C6 (step 4c) = {278/368}, no 5 -> R8C6 = {23}, 8 locked for R9, clean-up: no 5 in R8C2
11. 45 rule on N8 using R9C45 = 5, 3 remaining innies R789C6 = 18 = {279/369/378} (cannot be {567} because R8C6 only contains 2,3), no 5
11a. R8C6 = {23} -> no 2,3 in R7C6
11b. 9 of {369} must be in R7C6 -> no 6 in R7C6
12. Hidden killer pair 1,3 in R23C1 and R3C2 for N1, R3C2 = {13} -> R23C1 must contain one of 1,3 = {16/34}, no 2,5
12a. 2 in C1 only in R78C1, locked for N7, clean-up: no 8 in R6C2 (step 2a)
12b. 2 in C2 only in R56C2, locked for N4
13. 8 in C2 only in R78C2, locked for N7, clean-up: no 1 in R6C1
13a. 1 in C1 only in R23C1 = {16}, locked for N1 -> R1C1 = 8, placed for D\, R34C2 = [31]
13b. R1C1 = 8 -> R12C2 = 14 = {59}, locked for C2 and N1, clean-up: no 8 in R8C2
13c. Naked pair {67} in R89C2, locked for C2 and N7, clean-up: no 2 in R8C1
13d. R9C1 = 5, placed for D/, R8C1 = 4, R7C2 = 8 -> R6C2 = 2 (cage sum), R5C2 = 4, R67C1 = [72], clean-up: no 5 in R7C9
14. 8 on D/ only in R4C6 + R6C4, locked for N5 and 37(7) cage at R4C5
14a. 8 in N4 only in 16(3) cage at R4C3 = {268/358} -> R5C4 = {23}
15. 22(4) cage at R2C3 = {2578/4567} (cannot be {1678} because 1,8 only in R3C4) -> R23C3 = {27/47}, 7 locked for C3, R34C4 = {56}/[85], 5 locked for C4
15a. 5 in N8 only in R78C5, locked for C5
15b. Max R1C3 = 4 -> min R12C4 = 11, no 1 in R12C4
15c. R9C4 = 1 (hidden single in C4) -> R9C5 = 4
16. 45 rule on N8 using R9C45 = 5, 1 innie R7C6 = 1 outie R9C7 + 1, R7C6 = {79} -> R9C7 = {68}
16a. 7 in C7 only in R78C7, locked for 24(4) cage at R6C6 -> R7C6 = 9, R9C7 = 8
16b. 24(4) cage contains 7,9 = {3579}, no 4,6
17. R3C3 = 4 (hidden single on D\) -> R12C3 = [27]
17a. R23C3 = [74] = 11 -> R34C4 = 11 = {56}, locked for C4, clean-up: no 9 in R4C9
17b. R1C3 = 2 -> R12C4 = 13 = {49}, locked for C4 and N2
17c. Naked pair {56} in R3C49, locked for R3 -> R23C1 = [61]
17d. Naked pair {78} in R4C89, locked for R4 and N6
17e. 6 on D\ only in R4C4 + R5C5, locked for N5, CPE no 6 in R4C7
17f. Killer pair 5,6 in R3C9 and R78C9, locked for C9
18. R6C4 = 8 (hidden single on D/)
18a. R8C5 = 8 (hidden single in N8)
18b. 7 in C4 only in R78C4, locked for N8 -> R9C6 = 6, R8C6 = 3 (cage sum)
18c. R6C6 = 5, placed for D\ -> R2C2 = 9, placed for D\
and the rest is naked singles, without using the diagonals.