Answers for "wp get all terms"

wordpress get terms by taxonomy

You need to pass an additional argument to get_terms(). The default is to hide
"empty" terms-- terms which are assigned to no posts.

$terms = get_terms([
    'taxonomy' => $taxonomy,
    'hide_empty' => false,
]);

wordpress php cpt get all taxonomy

get_categories('taxonomy=taxonomy_name&type=custom_post_type');