[layoutIfNeeded]

Yep, the up vector is not necessarily orthogonal to the direction vector (which is also called “look at” vector in OpenGL [1]). Another approach would be to set

    y = up.reject(direction).normalized()

where

    a.reject(b) = a - b.project(a)

[1] https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml...