WP_Query meta_query >= date

What is missing? One tiny detail… And it’s easy to overlook…

the_field('datum_event');

Prints the field using the format you’ve defined in field settings. But… It has nothing to do with how the value of that field is stored in DB. ACF uses YYYYMMDD format when storing date values in DB. And WP_Query doesn’t use field format, since it looks directly in DB.

So you have to use other/raw format in your WP_Query:

$args = array(
    'post_type'  => 'agenda',
    'meta_query' => array(
        array(
            'key'     => 'datum_event',
            'value'   => '20190106',
            'compare' => '>='
        )
    ),
);
$loop = new WP_Query( $args );