A mol is a unit but also has a magnitude. How can a unit have a magnitude? And if mole is used to measure an amount of substance than what does mass measure?
Mole itself doesn't have a magnitude, but the value of mole does, in fact it is the magnitude. Any measurement has a magnitude (ie for the mass of 5 kg the magnitude will also be 5).
I think you are confusing it with scalar measurements (ie forces) which also have a direction. For example 5 Newtons 'in that direction'.
Mole is similar to a dozen (just a bit larger). It is used to count how many atoms, molecules, atoms or anything else there are.
If you think about mass as "the amount of stuff there is in an object" you can confuse it with mols
but the actual definition of mass is:
A property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.
which is different to mols (which is used to count objects).