custom-menu.php

<?php
 
function theme_menu($menu) { 
 
if ( has_nav_menu( $menu.'-menu' ) ) {
 
?>
 
<div id="<?php echo $menu ?>-menu"> <?php
 
    wp_nav_menu( array( 
  'theme_location' => $menu.'-menu', 
	'menu_class' => $menu, 
	));
	?>
    
</div> 
 
<?php
	}
}

Display-menu.php

<?php theme_menu('primary'); ?>

Register-Menu-in-WordPress.php

<?php

function theme_register_menus() {
    register_nav_menus(
        array(
            'primary-menu' => __( 'Primary Menu', 'text-domain' ),
            'secondary-menu' => __( 'Secondary Menu', 'text-domain' ), // you can repeat this as many times as you wish.
        )
    );
}

add_action( 'init', 'theme_register_menus' );