How to use modified (calculated) value of a field in Drupal entity query condition?
To do so you can use LIKE operator in your query like the following:
$host = parse_url($url_entered)['host'];
$result = \Drupal::entityQuery('node')
  -&gt;condition('type', 'ABC')
  -&gt;condition('field_link', &quot;%&quot; . $host . &quot;%&quot;, 'LIKE')-&gt;execute();

UPDATE
if you want to check that the exact host exist, you should select all values of your field and then compare with the entered host.
$host = parse_url($url_entered)['host'];
// Select all uris of field link.
$database = \Drupal::database();
$query = $database-&gt;select('node__field_link', 'nfl')
  -&gt;condition('nfl.bundle', 'page')
  -&gt;fields('nfl', ['field_link_uri']);
$result = $query-&gt;execute()-&gt;fetchAll(PDO::FETCH_COLUMN, 0);
$hosts = [];
// extract all hosts.
foreach ($result as $item){
  $hosts[] = parse_url($item)['host'];
}
// Check if the host already exist.
if (in_array($host, $hosts)){
  // Do what you want ici !
}