The functions such as get_categories
are unique to the post category taxonomy. “Category” is a taxonomy term. If you register your own taxonomies, you need to use get_terms which has similar parameters to your get_categories function.
$terms = get_terms(array(
'hide_empty' => false,
'orderby' => 'name',
'order' => 'ASC',
'taxonomy' => 'your-taxonomy'
));