This Wikipedia article gives that
If the unit vector along the axis is $e$, the moment of force about the axis is defined as $$M=e \cdot M = e \cdot (r \times F)$$
Then gives an example
which I read to be about the axis of unit vector $e_z$.
And then computes moment about axis $e_z$ as
$$M_z=e_z \cdot M = -Fx$$
So this is a moment about the axis of unit vector $e_z$. But does it make sense to have moment about axis $e_x$ (or $e_y$ for that matter) given the picture? Can one compute the moment about any axis?