Suggestion:
x = 1:7
m = x .* x'
7×7 Matrix{Int64}:
1 2 3 4 5 6 7
2 4 6 8 10 12 14
3 6 9 12 15 18 21
4 8 12 16 20 24 28
5 10 15 20 25 30 35
6 12 18 24 30 36 42
7 14 21 28 35 42 49
m[:, 1:end .∉ Ref((2,4,6))]
1 3 5 7
2 6 10 14
3 9 15 21
4 12 20 28
5 15 25 35
6 18 30 42
7 21 35 49