if (!key_exists('field', $displayData))
{
	return;
}

$field = $displayData['field'];
$fieldParams = $field->params;

Ok I see the problem, but this looks like a Joomla bug to me, because it should be loading the original mediajce.php file if the Layout is set back to "Default", but instead it appears to be loading components/com_fields/layouts/field/render.php

if (!key_exists('field', $displayData))
{
	return;
}

$field = $displayData['field'];
$fieldParams = $field->params;

if ($field->value == '') {
    return;
}

$value = $field->value;

// already processed...restart
if (strpos($value, '<') == 0) {
	$value = $field->rawvalue;
}

$text = basename($value);
$text = htmlentities($text, ENT_COMPAT, 'UTF-8', true);

$buffer = '';

// example attributes...
$attribs = array('class=""');

$element = '<img src="https://www.joomlacontenteditor.net/%s"%s alt="%s" />';

// not an image, so create a link
if (!preg_match('#\.(jpeg|jpeg|png|gif)$#', $value)) {
    $element = '<a href="https://www.joomlacontenteditor.net/%s"%s>%s</a>';
    
    // add blank target for links
    $attribs['target="_blank"'];
}

$buffer .= sprintf($element,
    htmlentities($value, ENT_COMPAT, 'UTF-8', true),
    implode(' ', $attribs),
    $text
);

echo $buffer;

<?php

defined('_JEXEC') or die;

use Joomla\Utilities\ArrayHelper;

if (empty($field->value) || empty($field->value['media_src']))
{
	return;
}

$value = $field->value['media_src'];

$text = basename($value);
$text = htmlentities($text, ENT_COMPAT, 'UTF-8', true);

$buffer = '';

// example attributes...
$attribs = array();

$element = '<img src="https://www.joomlacontenteditor.net/%s"%s alt="%s" />';

// not an image, so create a link
if (!preg_match('#\.(jpeg|jpg|png|gif)$#', $value)) {
    $element = '<a href="https://www.joomlacontenteditor.net/%s"%s>%s</a>';
    
    // add blank target for links
    $attribs['target'] = "_blank";
}

$buffer .= sprintf($element,
    htmlentities($value, ENT_COMPAT, 'UTF-8', true),
    ArrayHelper::toString($attribs),
    $text
);

echo $buffer;