WordPress Redirect from Custom Template

I need to redirect a custom template page to Homepage when a querystring key has an empty value.

for ex: https://example.com/customtemplatepage/?value=1 the Customtemplatepage is a page set with a custom template customtemplate.php in the root of the theme.

Whenever the querystring key "value" is empty it needs to be redirected to the root ("/" or homepage).

1. I tried to catch that in functions.php with add_action('wp_redirect','function');, but it is too early as global $template; is still empty / the customtemplate.php is not loaded yet
2. When I do it in customtemplate.php it is too late to use wp_redirect(); as the headers are already out there

It's possible to use JS with window.location in the customtemplate.php, but that's not an option as we have to do it server side.

The template_include filter should do the trick.

add_filter('template_include', function ($template) {
  // Get template file.
  $file = basename($template);

  if ($file === 'my-template.php') {
    // Your logic goes here.
    wp_redirect(home_url());
    exit;
  }

  return $template;
});

Out of curiosity, why redirect to the homepage? Is a 404 not meant for handling non-existent content?