How can I compute the flux and the inductance of a conductor in 3D projects?

In order to compute the inductance of a conductor, you need first to compute the flux through the conductor and then divide it by the value of the current in the conductor.

In order to compute the flux in coil conductor components you can use either the predefined computation:
Menu Advanced→ Predefined computation→ Magnetic flux→Compute flux through a coil conductor
or you can compute the surface integral of B on face(s) or grid2D:
Menu Advanced → Integral of a spatial quantity→Integral on face

Pay attention that the predefined computation gives the total value of the flux, while the surface integral gives a unit value that should be multiplied by the number of turns of the coil.

In order to compute the flux in solid conductors, you have to use the surface integral method.