Sums are for heights of cells (skyscrapers) visible from the edges. Only those higher than the previous one(s) count toward the sums.
Therefore each sum must include 9, the height of the highest skyscraper, which can be seen from each edge.
1. Upper sum in C7 = 10 -> R12C7 = [19]
1a. Right-hand sum in R2 = 22 -> R2C89 = 13 = [76/85]
1b. Upper total for C3 = 13 must be 4+9 (because no 1 in R1C3) -> R1C3 = 4, 9 in C3 cannot be below R5C3 because a maximum of three hidden skyscrapers, no 9 in R2C3 -> R2C3 must be hidden -> R2C3 = {123}
1c. 4 in N3 only in R3C789, locked for R3
2a. C1 and C5 are the only columns without upper totals specified -> 9 in R1 must be in R1C1 or R1C5 but cannot make right-hand sum in R1 = 18 with R1C1 = 9 (because then sum must see at least 2 in R1C9 and 8 in R1) -> R1C5 = 9
2b. R1 and R7 are the only rows without left-hand totals specified, no 9 in R1C1 -> R7C1 = 9
2c. C2 and C6 are the only columns without lower totals specified, no 9 in R9C2 -> R9C6 = 9
2d. R4 and R8 are the only rows without right-hand totals specified -> 9 in C9 must be in R4C9 or R8C9 but cannot make lower total in C9 = 21 with 9 in R8C9 -> R4C9 = 9
2e. Upper total in C9 = 18, R4C9 = 9 -> visible cells in R123C9 must total 9 -> R12C9 = [36] -> R2C8 = 7 (step 1a), R3C9 is hidden by R2C9 -> no 8 in R3C9
2f. R8C8 = 9 (hidden single in C8), lower total in C8 = 15 -> R9C8 = 6
2g. Lower total in C9 = 21, R4C9 = 9 -> visible cells must total 12 including 8 = [84] (because 3 already placed in C9) -> R9C9 = 4
2h. Right-hand total in R9 = 19, R9C689 = [964] = 19 -> R9C7 must be hidden -> no 7,8 in R9C7
2i. Right-hand total in R1 = 18, R1C5 = 9, R1C7 = 1 (hidden), R1C9 = 3 -> R1C6 = 6, R1C8 must be hidden -> R1C8 = 2, R3C9 = 5
2j. Naked pair {48} in R3C78, locked for R3
3a. Upper totals in C2 and C4 are greater than 17 -> no 8 in R1C24
3b. R1C1 = 8 (hidden single in R1)
3c. Lower totals in C3, C4 and C5 are greater than 17 -> no 8 in R9C345
3d. R9C2 = 8 (hidden single in R9)
3e. Left-hand total in R9 = 20, R9C2 = 8, R9C6 = 9 -> R9C1 = 3 (all other cells in R9 hidden by R9C2 = 8)
3f. Lower total in C1 = 18, R7C1 = 9, R9C1 = 3 -> R8C1 = 6
3g. Left-hand total in R8 = 22, R8C1 = 6, R8C8 = 9 -> remaining visible cell must be 7 -> no 8 in R9C4567
3h. R8C9 = 8 (hidden single in R8)
3i. 4 in N7 only in R8C2, locked for C2
3j. 1 in N9 only in R7C89, locked for R7
4a. Upper total in C2 = 20 -> visible cells must be [569] -> R1C2 = 5, R1C4 = 7
4b. Naked triple {123} in R2C123, locked for R2 and N1 -> R3C1 = 7, R3C23 = [69]
4c. From step 4a, 7 cannot be visible above the 9 -> no 7 in R45C2
4d. Left-hand total in R2 = 22, R2C7 = 9, visible cells must total 13 including 8 -> R2C123 = [213/231] -> R2C1 = 2
4e. Upper total in C6 = 30, R19C6 = [69] -> visible cells must be [78] -> no 8 in R24C6, no 7 in R78C6
4f. Upper total in C4 = 24, R1C4 = 7, visible cells must total 17 = [89] -> no 8 in R67C4
4g. Lower total in C4 = 24 cannot be [9654] because no 4 in R9C4 -> R5C4 = 9
4h. R6C2 = 9 (hidden single in N4), left-hand total in R6 = 14 -> R6C1 = 5
4i. Naked pair {14} in R45C1, locked for N4
4j. Naked pair {23} in R45C2, locked for C2 and N4 -> R2C23 = [13]
4k. Naked pair {47} in R78C2, locked for N7
4m. R9C5 = 7 (hidden single in R9)
5a. Left-hand total in R5 = 21, R5C4 = 9 -> visible cells must total 12 = [138/48] -> R5C3 = 8
5b. Right-hand total in R5 = 28, visible cells must total 19 and contain 7 which cannot be in R5C79 -> R5C6 = 7
5c. Lower total in C3 = 29, R35C3 = [98] -> visible cells must total 12 = [651/75] -> 5 in R89C3, locked for C3 -> R7C3 = 2
5d. Left-hand total in R4 = 33 cannot have 7 in R4C3 because R4C12 cannot total 9 -> R4C3 = 6, R6C3 = 7, R9C3 = 5 (step 5c), R9C47 = [12]
5e. R7C9 = 7 (hidden single in C9), naked pair {35} in R78C7, locked for C7 and N9
5f. R4C7 = 7 (hidden single in C7)
5g. Left-hand total in R4 = 33 must contain all of 6,7,8,9 (cannot just contain 6,8,9 because max R4C12 = 7) -> R4C8 = 8, remaining visible cells must total 3 -> R4C12 = [12], R5C12 = [43], R3C78 = [84], R567C8 = [531]
5h. Lower total in C7 = 37, R2345C7 = [9876], R9C7 = 2 -> remaining visible cells must be 5 -> R8C7 = 5
5i. Lower total in C4 = 24, R59C4 = [91] -> visible cells must total 14 -> R678C4 = [653]
5j. Right-hand total in R5 = 28, R5C4678 = [9765] -> R5C9 = 1
and the rest is naked singles.