Sliced Invoices: disable comments for all quotes

functions.php

add_filter( 'comments_open', 'si20220222_disable_comments_for_all_quotes', 10, 2 );
function si20220222_disable_comments_for_all_quotes( $open, $post_id = null ) {
	$_post = get_post( $post_id );
	if ( $_post && ( $_post->post_type === 'sliced_quote' ) ) {
		$open = false;
	}
	return $open;
}