Returning a custom content types with meta values

I think I am understanding your correctly…If I’m way off, let me know!

// Assuming ideas is an array and you are looking for ideas=>two
$query = new WP_Query(
    array(
        // You can pass 'any' to post_type, but you get a hold of revisions, attachments, and menu_items. But I am not sure how many Custom Post Types you have ¯\_(ツ)_/¯ 
        'post_type' => array('cpt_one', 'cpt_two', 'cpt_three', 'etc'),
        'meta_query' => array(
            array(
                'key' => 'ideas',
                'value' => array('one', 'two', 'three'),
                'compare' => 'IN'
            )
        )
    )
);

// ideas is still an array here, and the value of 'two' lives inside of that ideas array() 
$query = new WP_Query(
    array(
        'post_type' => array('cpt_one', 'cpt_two', 'cpt_three', 'etc'),
        'meta_query' => array(
            array(
                'key' => 'ideas',
                'value' => 'two',
                'compare' => 'LIKE' // Less-known and not explained well in the docs.
            )
        )
    )
);

Going back to Jacob Peattie’s point, querying can be heavy at times depending on the complexity of your arrays. Again, if I am off here….let me know!