menu_custom.php

<?php
/**
 * CUSTOM WP NAV MENU - no walker
 *
 * @package WordPress
 * @subpackage My theme
 *
 * @details custom replacement menu for wp_nav_menu()
 * with a "little" help from :
 * David Baker - https://dtbaker.net/
 * https://stackoverflow.com/questions/8840319/build-a-tree-from-a-flat-array-in-php
 * https://developer.wordpress.org/reference/functions/wp_get_nav_menu_items/
 */

/**
 * Menu function
 *
 * @param string $theme_location - registered theme menu locations.
 * @return void - output html for menu
 */
function my_theme_menu_f( $theme_location ) {

	$locations = get_nav_menu_locations();
	if ( ( $theme_location ) && $locations && isset( $locations[ $theme_location ] ) ) {

		// Get flat array of menu items with wp_get_nav_menu_items.
		$menu = get_term( $locations[ $theme_location ], 'nav_menu' );
		// If no menu object on theme location, abort.
		if ( is_wp_error( $menu ) ) {
			return;
		}
		$menu_id    = $menu->term_id;
		$array_menu = wp_get_nav_menu_items( $menu_id );
		// Another layer of checking.
		if ( empty( $array_menu ) ) {
			return;
		}

		// Extract only values needed
		// look up for all values with print($array_menu) ).
		$menu = array();
		foreach ( $array_menu as $m ) {
			$menu[ $m->ID ]               = array();
			$menu[ $m->ID ]['ID']         = $m->ID;
			$menu[ $m->ID ]['title']      = $m->title;
			$menu[ $m->ID ]['url']        = $m->url;
			$menu[ $m->ID ]['target']     = $m->target;
			$menu[ $m->ID ]['xfn']        = $m->xfn;
			$menu[ $m->ID ]['desc']       = $m->description;
			$menu[ $m->ID ]['classes']    = $m->classes;
			$menu[ $m->ID ]['attr_title'] = $m->attr_title;
			$menu[ $m->ID ]['parent']     = $m->menu_item_parent;
			$menu[ $m->ID ]['curr']       = $m->object_id;
			$menu[ $m->ID ]['children']   = array();

			$item_meta                 = get_post_meta( $m->ID );
			$menu[ $m->ID ]['urlargs'] = isset( $item_meta['menu-item-urlargs'] ) ? $item_meta['menu-item-urlargs'][0] : '';
			$menu[ $m->ID ]['mega']    = isset( $item_meta['menu-item-select-mega'] ) ? $item_meta['menu-item-select-mega'][0] : '';
			$menu[ $m->ID ]['icon']    = isset( $item_meta['menu-item-select-icon'] ) ? $item_meta['menu-item-select-icon'][0] : '';
		}

		// MAKE MULTIDIMENSIONAL ARRAY FROM FLAT ARRAY / CREATE MENU TREE.
		$menu_tree = my_theme_build_tree( $menu );
		// if error in build_tree function, abort.
		if ( empty( $menu_tree ) ) {
			return;
		}

		// Offcanvas theme location css selector to menu.
		$offc_css = '';
		if ( 'offcanvas-menu' === $theme_location ) {
			$offc_css = ' offcanvasopen';
		}

		// Start menu.
		echo '<ul class="navigation ' . esc_attr( $theme_location . $offc_css ) . '" id="' . esc_attr( $theme_location ) . '">';

		my_theme_build_menu( $menu_tree, $theme_location );

		echo '</ul>';

	}

}
add_action( 'my_theme_menu', 'my_theme_menu_f', 10, 1 );

if ( ! function_exists( 'my_theme_menuitem_elements' ) ) {
	/**
	 * Output menu items
	 *
	 * @param  array  $item - menu item.
	 * @param  string $theme_location - location in theme.
	 * @return void - echo $output html
	 */
	function my_theme_menuitem_elements( $item, $theme_location ) {

		// Current page id.
		$current_page_id = get_queried_object_id();

		$title      = ! empty( $item['title'] ) ? $item['title'] : '';
		$attr_title = ! empty( $item['attr_title'] ) ? ' title="' . esc_attr( $item['attr_title'] ) . '"' : '';
		$url        = ! empty( $item['url'] ) ? $item['url'] : '#';
		$target     = ! empty( $item['target'] ) ? ' target="' . esc_attr( $item['target'] ) . '"' : '';
		$xfn        = ! empty( $item['xfn'] ) ? ' rel="' . esc_attr( $item['xfn'] ) . '"' : '';
		$desc       = ! empty( $item['desc'] ) ? $item['desc'] : '';
		$classes    = ! empty( $item['classes'] ) ? implode( ' ', $item['classes'] ) : '';
		$current    = ! empty( $item['curr'] ) ? intval( $item['curr'] ) : '';
		$children   = ! empty( $item['children'] ) ? $item['children'] : array();
		// Custom meta for nav_menu_item CPT.
		$urlargs = ! empty( $item['urlargs'] ) ? $item['urlargs'] : '';
		$mega    = ! empty( $item['mega'] ) ? $item['mega'] : '';
		$icon    = ! empty( $item['icon'] ) ? $item['icon'] : '';

		// Theme locations (Offcanvas or Vertical) submenu arrow indicator.
		$arr = '';
		if ( 'offcanvas-menu' === $theme_location || 'vertical-menu' === $theme_location ) {
			$arr = '<a href="#" class="sub"><i class="typcn typcn-chevron-right" aria-hidden="true"></i></a>';
		}
		// CSS classes for menu list item.
		$item_class = '';
		if ( $current_page_id === $current ) {
			$item_class .= ' current';
		}
		$item_class .= my_theme_subs( $children, $mega );

		// OUTPUT MENU ITEM ELEMENTS.
		$output  = '<li class="menu-item' . esc_attr( $item_class ) . '">';
		// $urlargs var is custom meta defined.
		$output .= '<a href="' . esc_url( $url . $urlargs ) . '" class="menu-link ' . esc_attr( $classes ) . '" ' . $attr_title . $target . $xfn . '>';
		// $icon var is custom meta defined
		$output .= ( $icon ? '<i class="item-icon typcn ' . esc_attr( $icon ) . '"></i>' : '' );
		$output .= ( $title ? '<span class="title">' . esc_html( $title ) . '</span>' : '' );
		$output .= ( $desc ? '<span class="desc">' . esc_html( $desc ) . '</span>' : '' );
		// $mega var is custom meta defined
		$output .= ( ( ! empty( $children ) || $mega ) ? '<span class="append-sub-arrow"></span>' : '' );
		$output .= '</a>';
		$output .= ( ! empty( $children ) ? wp_kses_post( $arr ) : '' );

		echo wp_kses_post( $output );
	}
}

if ( ! function_exists( 'my_theme_subs' ) ) {
	/**
	 * CSS Class if there are children
	 *
	 * @param array  $children - sub items of menu.
	 * @param string $mega - ID of megamenu (if any).
	 * @return $css
	 */
	function my_theme_subs( $children, $mega ) {
		$css = '';
		if ( ! empty( $children ) || $mega ) {
			$css = ' dropdown';
		}
		return $css;
	}
}

if ( ! function_exists( 'my_theme_build_tree' ) ) {
	/**
	 * Build tree menu ( multidimensional array )
	 *
	 * @param array   $elements - array of elements.
	 * @param integer $parent_id - ID of parent item.
	 * @return $branch
	 */
	function my_theme_build_tree( array &$elements, $parent_id = 0 ) {
		$branch = array();

		foreach ( $elements as $element ) {
			if ( $element['parent'] == $parent_id ) {
				$children = my_theme_build_tree( $elements, $element['ID'] );
				if ( $children ) {
					$element['children'] = $children;
				}
				$branch[ $element['ID'] ] = $element;
				//unset($elements[$element['ID']]);
			}
		}
		return $branch;
	}
}

if ( ! function_exists( 'my_theme_build_menu' ) ) {
	/**
	 * Build menu
	 *
	 * @param array  $menu_tree
	 * @param string $theme_location
	 * @return html
	 * Recursive function to print out multidimensional array
	 * as menu in nested unordered list format
	 */
	function my_theme_build_menu( array &$menu_tree, $theme_location ) {

		foreach ( $menu_tree as $id => $branch ) {

			my_theme_menuitem_elements( $branch, $theme_location );

			$children = ! empty( $branch['children'] ) ? true : false;
			$mega     = ! empty( $branch['mega'] ) ? $branch['mega'] : '';
			if ( $children || isset( $mega ) ) {

				// If megamenu is set in custom meta
				// AND theme location is hor. menu, render mega menu.
				if ( $mega && 'horizontal-menu' === $theme_location ) {
					echo '<ul class="sub-menu mega-menu">';
					echo apply_filters( 'my_theme_render_mega_menu', $mega );
				} else {
					echo '<ul class="sub-menu">';
					my_theme_build_menu( $branch['children'], $theme_location );
				}
				echo '</ul>';

			}

			echo '</li>';
		}

	}
}

An alternative to WP menu walker. Use at your own risk, but this served well for Micemade themes.
Usage: do_action( 'my_theme_menu', 'my-menu-name' );
Remove unnecessarry vars or funcs ( custom meta - $icon $mega,$urlargs , my_theme_render_mega_menu action ... etc. )
Feel free to suggest a better solution(s) or improvements.