I think you might misunderstand the docs, as the specified dim should have the size 3 and you can use multiple dimensions as seen here:
a = torch.randn(4, 5, 6, 7, 8, 3)
b = torch.randn(4, 5, 6, 7, 8, 3)
torch.cross(a, b, dim=5)

For your example it won’t work, since your last dimension has a size of 2.