For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
Which one? Did you try with a standard J!4 template?In my template
<?php
$app = Joomla\CMS\Factory::getApplication();
$messageSuccess = $app->getMessage('message');
$messageError = $app->getMessage('error');
if (!empty($messageSuccess)) {
echo '<div id="meser" class="alert alert-success">' . $messageSuccess . '</div>';
}
if (!empty($messageError)) {
echo '<div id="meser" class="alert alert-danger">' . $messageError . '</div>';
}
?>