Query arguments to get posts with multiple authors

Hi, I am trying to modify a WordPress query to return posts where a given user is among the authors.

I would expect it to work with:

$args = array(
'author__in'     => $authors,
);

That works fine for posts with only one author, but if multiple authors is assigned to a post, it only returns those where the author is mentioned first (in the list of multiple authors of the post).

Please advice how to modify the query to get all posts where a given author is assigned.

Thank you.

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