As I was told above in the comment, WP_User_Query does not support the nested sub-arrays… So at the end I solved the thing by separated queries…
Not sure whether there is more efficient way, but in case somebody needs an inspiration, below is my solution of the problem.
// get ids of first set of users
$authors_query = new WP_User_Query(
array(
'fields' => 'id',
'role' => 'author',
'exclude' => array(36, 41)
)
);
$authors = $authors_query->get_results();
// get ids of second set of users
$admins_query = new WP_User_Query(
array (
'fields' => 'id',
'include' => array(23, 45),
)
);
$admins = $admins_query->get_results();
// merge ids
$user_ids = array_merge( $admins, $authors );
// get final selection
$user_query = new WP_User_Query(
array(
'include' => $user_ids,
'orderby' => 'display_name',
'order' => 'ASC',
)
);