I understand where you're coming from, as the definition of formula unit can be a bit confusing at first.
Here's a little more detail on the difference between formula unit and empirical formula:
Formula unit is the simplest ratio of atoms in a chemical compound, without regard to the arrangement of atoms in the molecule. It represents the minimum number of atoms required to make up a chemical compound.
Empirical formula, on the other hand, represents the simplest whole-number ratio of atoms in a molecule. This means that the empirical formula shows the relative number of atoms in a molecule, but not the actual number of atoms.
For example, let's take the compound methane (CH4). The formula unit for methane would be CH4, as this represents the simplest ratio of atoms (one carbon atom and four hydrogen atoms). The empirical formula for methane would be CH2, as this represents the simplest whole-number ratio of atoms (one carbon atom and two hydrogen atoms).
I hope this clears things up a bit.