php, using require_once() properly

I have a page with a variable and a function:

test.php

<?php
  $myVar = "myVar";
  
  function myFunc() {
    echo "myFunc()";
  }
?>

The first page that includes it, can see the variable value.

<?php
  echo "page1";
  require_once("include/test.php");
  print_r($myVar);

function GoTo2() {
  $urlSite = "page2.php";
  include($urlSite); 
  exit();
}

GoTo2();
?>

but the second page, cannot see the variable.

<?php
  echo "page2n";
  require_once("include/test.php");
  print_r($myVar);
?>

it generates PHP Warning: Undefined variable $myVar in .../page2.php on line 4

I cannot use require() in the second page, because it generates an error – PHP Fatal error: Cannot redeclare myFunc() (previously declared in .../include/test.php) in .../include/test.php ...

What is the proper php way that both pages can see the variable and also can use the function?

EDIT:

• this is a simplified of my real pages. I just discovered that page2 cannot see the variable when the site was upgraded to php8, and I recieved all “Undefined variable” warnings.
• page1 is a “dispatcher” page
• suppose I inherited this code from another developper, what is the best solution to solve the problem?