function ssm_register_post_type() {
    register_post_type( 'new_sermons', [
        'labels'       => [ /* … */ ],
        'public'       => true,
        // change these:
        'has_archive'  => 'new-sermons',
        'rewrite'      => [ 'slug' => 'new-sermons', 'with_front' => false ],
        'show_in_rest' => true,
        'supports'     => [ 'title','editor','thumbnail' ],
    ]);
}