Apparently, when rendering the Map Block at the front end, some html formatting is added to the javascript code which breaks everything:
<div class="wp-block-advanced-gutenberg-blocks-gmap">
<script>
function initMap2137589149() {</p>
<p> var coords = { lat: 51.66094, lng: 8.348746 }</p>
<p> var map = new google.maps.Map( document.querySelector( '#gutenblock-gmap-2137589149' ), {
zoom: 14,
center: coords,
styles: "default" } );</p>
<p> var marker = new google.maps.Marker( {
position: coords,
map: map
} );</p>
<p> var infoWindow = new google.maps.InfoWindow( {
content: "</p>
<p><strong>Conrad-Hansen-Musikschule</strong></p>
<p>Von-Galen-Platz 1, 59557 Lippstadt, Allemagne</p>
<p>"
} )</p>
<p> marker.addListener('click', function() {
infoWindow.open( map, marker );
} )
}
</script>