WordPress at a glance
filter is not described

block_categories filter-hook . WP 5.0.0

Filter the default array of block categories.

Usage

add_filter( 'block_categories', 'filter_function_name_2070', 10, 2 );
function filter_function_name_2070( $default_categories, $post ){
	// filter...

	return $default_categories;
}
$default_categories(array)
Array of block categories.
$post(WP_Post)
Post being loaded.

Where the hook is called

get_block_categories()
block_categories
wp-admin/includes/post.php 2182
return apply_filters( 'block_categories', $default_categories, $post );

Where the hook is used (in WP core)

Does not used.