get taxonomies from terms

Question

I have two post types

1. Documents
2. News Items

with categories for each post type,

1. Documents -- PDF, Word, Excel
2. News Items -- Articles, Releases

BUT they share the same tags.

1. Documents -- BOSS, EFF, CDF
2. News Items -- BOSS, EFF, CDF

How can I retrieve a list of the categories whose posts( or post count. regardless of post type) have a specified tags e.g.

BOSS -- PDF(2), Releases (1)

CDF -- Articles (1), Excel (1)

Answer 1

After some research I came up with the following

// Get the posts in that category with the required tag
$args = array(
    'post_type' => ['documents','news'],
    'fields'          => 'ids', // Only get post IDs
    'posts_per_page'  => -1,
    'tax_query'      => array(
        array(
            'taxonomy'  => 'forms',
            'field'     => 'slug',
            'terms'     => $symbol
        )
    )
);
$posts_array = get_posts( $args );
$categories = wp_get_object_terms($posts_array, ['sources','articles'], ['fields' => 'id=>name']);