Global Scope fails for included file - php

Question

Can someone please help me with a scoping issue. I've been looking at this for so long and I just don't see why this isn't working:
connection.php
<?php
$hostname = "xxx.xxx.xxx.xxx";
$username = "xxxxxxxx";
$password = "xxxxxxxx";
$db_name = "xxxxxxxx";
function isSecure() {
return (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off')
|| $_SERVER['SERVER_PORT'] == 443;
}
global $link;
$link = mysqli_connect($hostname, $username, $password, $db_name);
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
exit();
}
?>
builder.php
<?php
$path = $_SERVER['DOCUMENT_ROOT'];
$connection = $path . '/scripts/connection.php';
include_once ($connection);
session_start();
$club_id = $_SESSION['club_id'];
if (mysqli_connect_errno()) {
trigger_error("Failed to connect to MySQL: " . mysqli_connect_error());
exit();
}
$sql = "SELECT * FROM Workout_types
WHERE club_id=$club_id
ORDER BY type";
$result = mysqli_query($link, $sql) or trigger_error("Error description:" . mysqli_error($link) . "done");
?>
and I get the dreaded
mysqli_query() expects parameter 1 to be mysqli, null given in...
error.
Implementing the troubleshooting tips below, I changed a couple of lines.
builder.php:
require_once ("../scripts/connection.php");
connection.php:
if (!$link) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
exit();
}
It still doesn't work, but the errors are a bit different:
PHP Warning: mysqli_query(): Couldn't fetch mysqli in G:\PleskVhosts\example.com\httpdocs\workouts\builder.php on line 114
PHP Warning: mysqli_error(): Couldn't fetch mysqli in G:\PleskVhosts\example.com\httpdocs\workouts\builder.php on line 114
PHP Notice: Error description:done in G:\PleskVhosts\example.com\httpdocs\workouts\builder.php on line 114
where line 114 is the mysqli_query line.
I checked the GoDaddy docs, and that path is correct.
Just to prove that my include path was correct, I added this to connection.php:
global $test;
$test = "hello world";
Then in builder.php, I added a line echo $test;, and it printed hello world with no trouble whatsoever.
I should mention two other things could be helpful:
The code that I posted for builder.php is embedded in html code for a web page. It's the only php code in that file.
I originally wrote this code about 5 years ago, and it's been functioning flawlessly until I upgraded the php version on my server from 5.6.40 to 7.3.27. That's when it began to fail.