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You need to specify the return-format of the acf-field as ‘l’

enter image description here

& then modify your query as follows: 

$todayName = date('l');
$schedules = new WP_Query([
  'posts_per_page' => -1,
  'post_type' => 'serie',
  'meta_query' => [
    'relation'    => 'AND',
    [
      'key'   => 'status',
      'value'     => '1',
      'compare'   => '=',
    ],
    [
      'key'   => 'release_date' ,
      'value' => '"'.todayName.'"',
      'compare' => 'LIKE', 
      // You might try this too. If you can use this instead of `LIKE` please do, because it's more efficient
      // 'value' => todayName,
      // 'compare' => '=',      
    ]
  ]
]);