if Fixed Update calls outside functions

Imagine all variables and custom functions are declared and defined in Awake, but called from within Update, or FixedUpdate for the physics functions.

If my understanding is correct, functions don’t do work until they are called, and Unity calls Update and FixedUpdate (and their content) by frame and by time respectively, and it is the priority with which Unity handles them (and their content) that makes FixedUpdate preferable for physics.

So if Update content calls only functions not related to physics, and FixedUpdate content calls only physics functions, why does it matter where the functions are described?

Your question is somewhat confusing… it doesn’t matter where a function is declared in your script (although you can’t declare a function inside another function so your description of declaring a function inside Awake() is incorrect). So you can place the function definition:

private void MyMethod() { ... }

At the top of your script, underneath Start(), right at the end - it makes no difference. Whatever you do inside MyMethod will only happen when the method is called, which could be:

void Start() {
  MyMethod();
}

or:

void OnMouseClick() {
  MyMethod();
}

or:

void FixedUpdate() {
  MyMethod();
}