And what happens when you don’t have STP?
Answer: you get a distribution which leads to statistical matters because external changes are never STP in practice.
STP is merely to provide a reference point. Everything in reality fluctuates and when you have to measure or estimate matters under non-controlled lab conditions, you have to use statistics QED.
I can see you have a high school/college level understanding of chemistry. Maybe you’re a HS Chem teacher. Good for you.
But at higher levels of science, statistical methods are crucial. Case in point: the Heisenberg principle.
I guess you didn’t read the followup. It is MASS only. volume temperature and pressure are dependent variables. Mass is not.
It doesn’t matter if it is nitrogen or uranium or gold, or any other atomic element or molecule or any phase. The Avogadro number is always 6.22*10^23.