Code Snippet - https://solusipress.com/sisi-koding-wordpress-custom-taxonomy/

snippet-1.php

<?php
function filter_events_by_taxonomies( $post_type, $which ) {
	if ( 'event' !== $post_type )
		return;
	$taxonomies = array( 'event_category', 'event_location' );
	foreach ( $taxonomies as $taxonomy_slug ) {
		$taxonomy_obj = get_taxonomy( $taxonomy_slug );
		$taxonomy_name = $taxonomy_obj->labels->name;
		$terms = get_terms( $taxonomy_slug );
		echo "<select name='{$taxonomy_slug}' id='{$taxonomy_slug}' class='postform'>";
		echo '<option value="">' . sprintf( esc_html__( 'Show All %s', 'text_domain' ), $taxonomy_name ) . '</option>';
		foreach ( $terms as $term ) {
			printf(
				'<option value="%1$s" %2$s>%3$s (%4$s)&lt;/option>',
				$term->slug,
				( ( isset( $_GET[$taxonomy_slug] ) && ( $_GET[$taxonomy_slug] == $term->slug ) ) ? ' selected="selected"' : '' ),
				$term->name,
				$term->count
			);
		}
		echo '</select>';
	}
}
add_action( 'restrict_manage_posts', 'filter_events_by_taxonomies' , 10, 2);