but then the check of the 3x3 subgrids will not total 45 they they have to

You could still have [9, 9, 9, 9, 9, 0, 0, 0, 0, 0] == 45 be true while having all values in the range 1 to 9

I'd like to mention in the kata description it is already clearly stated that the input is from [1, 9] list. BTW I liked your keen attention.

What if I have a sudoku row like [1,1,1,3,4,5,6,7,8,9], isnt the sum 45 anyway? or just [45, 0 ,0, ...]?

This is the second comment that claims O(n^2). Is linear time complexity really that difficult to recognize? You should definitely have a firm grasp of time complexity before criticizing people about it.

This is about O(2n) and O(n) amortized.

How is it O(n²)? Depending on the memory allocation algorithm it might be (but I think it's very unlikely) but it's implementation-defined.

this is a clerver solution but not a besetpractices solution

Kata description says:

keep it as simple as possible

meh. it works but you not really pushing an iteam to a List.