Thank you very much,
in doing is what I have tried to write a little complicated.

I use the theme Bizlight Pro. Since I lacked a function in the blog, I have written for a plugin.

<?php
add_action('the_content','dsgvo_ansichten');
add_filter( 'the_content', 'wpautop' , 99);

function dsgvo_ansichten($content){
	$MyType = get_post_type( get_the_ID() );
	$customs = get_post_custom(get_the_ID());
	if($MyType == 'dsgvo'){
		$dsgvo_Content = '';
		$derTitel = 'DS-GVO Artikel' ; //the_title;
		if (array_key_exists('_Nummer', $customs)) {
		$nummer = $customs['_Nummer'][0];
		} else {
			$nummer='';
		}
		$dsgvo_Content = '<h2>'.$derTitel.' '.$nummer.'</h2>'.$content;
		
		//Nummern von den ErwGründen auslesen
		if (array_key_exists('_ErwGrund', $customs)) {
		$_ErwGrund = $customs['_ErwGrund'][0];
		} else {
			$_ErwGrund='';
		}
		
		$myNumbers = ['relation' => 'OR'];
		
		// *** String zerlegen ***
		$teile = explode(",", $_ErwGrund);
		
		foreach($teile as $teil){
			$einteil = explode("-", $teil);
			if(count($einteil)==2){
				for ($i = $einteil[0]; $i <= $einteil[1]; $i++) {
					$myNumbers[] = ['key' => '_Nummer', 'value' => $i];
				}
			} else {
					$myNumbers[] = ['key' => '_Nummer', 'value' => $teil];
			}
		}

		
		// ***  String zerlegt ***
		
		$args = array(
			'post_type' => 'erwgrund',
			'meta_query' => $myNumbers, 
			'orderby' => '_ErwGrund',
			'order' => 'ASC',
			'posts_per_page' => 40);
		$postslists = get_posts( $args );	
		$dsgvo_Content .= '<hr><h2>Die Erwägungsgründe</h2>';
		if ( $postslists ) {
			foreach ( $postslists as $postslist ) {
					$dsgvo_Content .= '<h3>'.$postslist->post_title.'</h3>'.$postslist->post_content.'<br/><br />';
			}
		}
		wp_reset_postdata();
		return $dsgvo_Content; 
	} 
	
	if($MyType == 'erwgrund') { 
		$nummer = $customs['_Nummer'][0];
		$ErwGrund = $customs['_ErwGrund'][0];
		$Sum = '<div><h2>Erwägungsgrund '.$nummer.'</h2><br />'.$content;
		$Sum .= '<br><hr><h2>gehört zur DS-GVO Artikel:'.$ErwGrund.'</h2></div>';
		// Den Artikel dazu laden und dem String anhängen	
		$args = array('post_type' => 'dsgvo', 'meta_query' => array(array('key' => '_Nummer', 'value' => $ErwGrund)));
		$postslists = get_posts( $args );
		wp_reset_postdata();
		if ( $postslists ) {
			foreach ( $postslists as $postslist ) {
				$Sum .= '<p>'.$postslist->post_content.'</p>';
			}
		}	
		return $Sum; 
	}
	
	if($MyType <> 'erwgrund' AND $MyType <> 'dsgvo' ){
		return $content;
	}
}
?>

Unfortunately, now is not working the comments.
URL:
https://www.e-dsb.de/dsgvo/ds-gvo-artikel-1/

Now I want to enable comments again.
Is that something intelligible?