I enjoyed finding the clashes with R9C5 and R9C6.
Prelims
a) R23C4 = {19/28/37/46}, no 5
b) R23C5 = {39/48/57}, no 1,2,6
c) R34C1 = {14/23}
d) R4C45 = {17/26/35}, no 4,8,9
e) R45C9 = {69/78}
f) R78C1 = {18/27/36/45}, no 9
g) 14(2) cage at R8C2 = {59/68}
h) 20(3) cage at R1C6 = {389/479/569/578}, no 1,2
i) 19(3) cage at R2C6 = {289/379/469/478/568}, no 1
j) 23(3) cage at R6C4 = {689}
k) 8(3) cage at R6C7 = {125/134}
l) 18(5) cage at R1C2 = {12348/12357/12456}, no 9
m) and, of course, 45(9) cage at R6C1 = {123456789}
1a. 8(3) cage at R6C7 = {125/134}, 1 locked for R6 and N6
1b. 23(3) cage at R6C4 = {689}, CPE no 6,8,9 in R45C5, clean-up: no 2 in R4C4
1c. 45 rule on N9 2 outies R9C56 = 3 = {12}, locked for R9, N8 and 19(5) cage at R8C7
1d. 45(9) cage at R6C1 = {123456789}, 1 locked for R7 and N7, clean-up: no 8 in R78C1
1e. 45 rule on R6789 2 innies R6C36 = 12 = {39/48/57}, no 1,2,6
1f. 18(5) cage at R1C2 = {12348/12357/12456}, CPE no 1,2 in R1C1
1g. R7C5 ‘sees’ R7C2346 + R8C456 of 45(9) cage at R6C1 -> whichever of 6,8,9 is in R7C5 must also be in R6C12
1h. 45 rule on R789 2 outies R6C12 = 1 innie R7C5 -> R6C12 = {26/28/29}, 2 locked for R6, N4 and 45(9) cage, clean-up: no 3 in R3C1, no 5 in 8(3) cage at R6C7
1i. R6C36 = {57} (hidden pair in R6)
1j. Naked pair {57} in R6C36, CPE no 5,7 in R3C3 using D\
1k. Naked triple {134} in 8(3) cage at R6C7, 3,4 locked for N6
1l. Combined cage R34C1 + R78C1 = {14}{27}/{14}{36}/[23]{45}, 4 locked for C1
1m. Combined cage R6C4 + 14(2) cage at R8C2 = 6{59}/8{59}/9{68}, 9 locked for D/
1n. 45 rule on D\ 3 innies R4C4 + R5C5 + R6C6 = 14 = {257/347/356} (cannot be {167} = [617] because R45C5 = [12] clashes with R9C5), no 1, clean-up: no 7 in R4C5
1o. 7 of {257/347} must be in R6C6 (cannot be [725] because R45C5 = [12] clashes with R9C5), no 7 in R4C4, clean-up: no 1 in R4C5
1p. 2,4 of {257/347} must be in R5C5 -> no 7 in R5C5
1q. Hidden killer pair 8,9 in 17(3) cage at R1C1 and 14(3) cage at R7C7 for D\, neither cage can contain both of 8,9, no 8,9 in R4C4 + R5C5 + R6C6 -> each cage must contain one of 8,9
1r. 14(3) cage at R7C7 = {149/158/248} (cannot be {239} which clashes with R4C4 + R5C5 + R6C6), no 3,6,7
1s. Killer pair 4,5 in R4C4 + R5C5 + R6C6 and 14(3) cage, locked for D\
1t. Hidden killer pair 1,2 in 14(3) cage and 15(3) cage at R5C8 for N9, 14(3) cage contains one of 1,2 -> 15(3) cage must contain one of 1,2 = {159/249/258/267} (cannot be {168} which clashes with 14(3) cage), no 3
1u. Consider combinations for R4C45 = {35}/[62]
R4C45 = {35}, locked for N5
or R4C45 = [62] => R5C5 + R6C6 = [35]
-> 3,5 in R4C45 + R5C5 + R6C6, locked for N5, no 5 in R5C5
1v. 7 in N5 only in R456C6 + R5C4, CPE no 7 in R5C7
1w. 7 in N6 only in R4C789 + R5C89, CPE no 7 in R23C9
2a. 45 rule on N36 3+1 innies R1C78 + R25C7 = 28
2b. Max R1C78 + R2C7 = 24 -> no 2 in R5C7
2c. Max R125C7 = 24 -> min R1C8 = 4
2d. 2 in N6 only in R4C78 + R5C8, locked for 27(6) cage at R2C9, no 2 in R2C9 + R3C89
2e. Min R5C7 + R6C6 = 11 -> max R4C6 + R5C56 = 11, no 9 in R5C6
2f. R4C4 + R5C5 + R6C6 (step 1n) = {257/356} (cannot be {347} = [347] because R45C6 + R5C7 = 11 = {12}8 clashes with R9C6), no 4, 5 locked for N5 and D\, clean-up: no 3 in R4C4
2g. Naked pair {23} in R45C5, locked for C5, 2 locked for N5 -> R9C56 = [12], clean-up: no 9 in R23C5
2h. 4 on D\ only in 14(3) cage at R7C7, locked for N9
2i. 3 in N9 only in 19(5) cage at R8C7 = {12358/12367}, no 9
2j. 1 in C6 only in R45C6, locked for N5
2k. Hidden killer pair 1,2 in R1C4 and R23C4 for N2, neither can contain both of 1,2 -> R1C4 = {12}, R23C4 = {19/28}
2l. 19(3) cage at R2C6 = {379/469/478/568} (cannot be {289} which clashes with R23C4), no 2
2m. 2 in N3 only in 12(3) cage at R1C9, locked for D/ -> R5C5 = 3, placed for both diagonals, R4C5 = 2, R4C4 = 6, placed for D\, R6C6 = 5, R6C3 = 7, clean-up: no 9 in R5C9
2n. Naked pair {89} in R6C45, locked for R6, N5 and 23(3) cage at R6C4 -> R5C4 = 4, R7C5 = 6, clean-up: no 3 in R8C1
2o. Naked pair {17} in R45C6, 7 locked for C6, R5C5 = 3, R6C6 = 5 -> R5C7 = 6 (cage sum), clean-up: no 9 in R4C9
2p. Naked pair {78} in R45C9, locked for C9 and N6
2q. Naked pair {59} in R4C78, locked for R4, C6 and 27(6) cage at R2C9
2r. 27(6) cage at R2C9 = {123579/124569} (only combinations containing 2,5,9), no 8, 1 locked for N3
2s. 2 in N3 only in 12(3) cage at R1C9 = {246} (only remaining combination), 4,6 locked for N3 and D/, clean-up: no 8 in 14(2) cage at R8C2
2t. Naked pair {13} in R23C9, locked for C3 and N3 -> R3C8 = 7, R6C9 = 4, R9C9 = 9, placed for D\, R7C7 + R8C8 = [41], 1 placed for D\, 12(3) cage = [642], 17(3) cage at R1C1 = [728], R6C78 = [13], 14(2) cage = [95], R7C3 = 1, 1,9 placed for D/ -> R45C6 = [71], R6C45 = [89], naked pair {19} in R23C4, locked for N2, 9 locked for C4 -> R1C4 = 2, clean-up: no 5 in R2C5, no 2 in R7C1, no 2,4 in R8C1
2u. R1C2 = 1 (hidden single in R1) -> R34C1 = [41], R3C5 = 5 -> R2C5 = 7
2v. Naked pair {25} in R78C9, locked for N9
and the rest is naked singles.