Change meta-box title- “LearnDash Quiz Settings” to “Quiz Settings”

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: