how to display all categories in wordpress?

In the code you gave us you are selected the categories selected for the specific post get_the_ID() is doing that part. However you would be best off using another function get_categories() https://developer.wordpress.org/reference/functions/get_categories/ which you would do like so:

$categories = get_categories();foreach($categories as $category) {   echo '<div class="col-md-4"><a href="' . get_category_link($category->term_id) . '">' . $category->name . '</a></div>';}

You can also pass through arguments to be more specific (if needed) - see https://developer.wordpress.org/reference/functions/get_terms/ for details on what you can pass through

like this :

<?php$categories = get_categories( array(    'orderby' => 'name',    'order'   => 'ASC') );foreach( $categories as $category ) { echo '<div class="col-md-4"><a href="' . get_category_link($category->term_id) . '">' . $category->name . '</a></div>';   } 

You can also use wp_list_categories and pass arguments to it to show only what you need. A full list of arguments can be found in the codex: https://developer.wordpress.org/reference/functions/wp_list_categories

This will output all categories (even if they're empty) indented to indicate hierarchy.

$args = array(    'child_of'            => 0,    'current_category'    => 0,    'depth'               => 0,    'echo'                => 1,    'exclude'             => '',    'exclude_tree'        => '',    'feed'                => '',    'feed_image'          => '',    'feed_type'           => '',    'hide_empty'          => 0,    'hide_title_if_empty' => false,    'hierarchical'        => true,    'order'               => 'ASC',    'orderby'             => 'name',    'separator'           => '<br />',    'show_count'          => 0,    'show_option_all'     => '',    'show_option_none'    => __( 'No categories' ),    'style'               => 'list',    'taxonomy'            => 'category',    'title_li'            => __( 'Categories' ),    'use_desc_for_title'  => 1,);var_dump( wp_list_categories($args) );