You can do this via the available translation filters:
add_filter( 'gettext_with_context', 'gowp_replace_learndash_label', 10, 4 );
function gowp_replace_learndash_label( $translation, $text, $context, $domain ) {
if (
( 'LearnDash %s Settings' == $text ) &&
( 'placeholder: Quiz' == $context ) &&
( 'learndash' == $domain )
) {
$translation = str_replace( 'LearnDash ', '', $translation );
}
return $translation;
}
This removes “LearnDash ” from the string:
You can also remove the first condition of the if-check to have this removed from all of the metaboxes: