Is there another way to retrieve a post_id from post_meta other than a SQL query?

Why are you using wp_list_pluck?
In your query, you use 'fields' => 'ids' so the return is an array of found post ids.

From the codex:

‘ids’ – Return an array of post IDs.

Try returning $post_query->posts;

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)