As discussed here: https://www.tinyportal.net/index.php?topic=37008.0

This RSS feed does not produce an output in an RSS block
https://www.tinyportal.net/index.php?topic=37008.0

This link does:
https://feeds.rijksoverheid.nl/nieuws.rss

Checking the code I see the function TPparseRSS does not return an output when calling fetch_web_data($backend);

function TPparseRSS($override = '', $encoding = 0)
{
global $context, $smcFunc, $sourcedir;

// Initialise the number of RSS Feeds to show
$numShown = 0;

$backend = isset($context['TPortal']['rss']) ? $context['TPortal']['rss'] : '';
if ($override != '') {
	$backend = $override;
}

require_once $sourcedir . '/Subs-Package.php';
$data = fetch_web_data($backend); <<<<<<
$xml = simplexml_load_string($data);

I am not sure what the problem is, I do no not understand the code in the SMF file Subs.php and why it does not return a result.