ACF Wordpress meta_query for taxonomy categories doesn't work

I have the problem not to get the meta_query working.

Category 5 are ContactPersons with an ACF 'bereich' for a category.

This is the code:

$cat=wp_get_post_categories( get_the_ID(), array( 'fields' => 'ids' ) );
 array_pop($cat);
 $c = get_posts(array(
        'numberposts'   => -1,
        'post_type'     => 'post',
        'category'      => 5,
        'meta_query'            => array(
        array(
                'key' => 'bereich',
                'value' => $cat,
                'compare' => '='
                )
        )
        

        ));
}

field 'bereich' is an array of taxonomy category and same looking the $cat. The array_pop … I know the system 2 elements, just need one than its the same as 'bereich'. LIKE brings me all of the parent. IN also doesn't work.

I also tried this:

$c = get_posts(array(
        'numberposts'   => -1,
        'post_type'     => 'post',
        'category'      => 5,
        'tax_query' => array(array('taxonomy' => 'category', 'field' => 'slug', 'terms' => $cat)),));
}

It does not work!

Please help,

Tom