Is it possible to have a Faceted Navigation/Filters on a Product Tag page?

I suggest evaluating the premium plugin FacetWP (I am not affiliated with them), that supports faceted navigation and filters for WooCommerce too. https://facetwp.com/using-facetwp-with-woocommerce/ Or any other similar plugin of course, I know only FacetWP myself. As for the second question, I think that such plugins manage the display of specific filters automatically, excluding non-pertinent ones.

How to create a sub-page of sub-page?

I may be completely misunderstanding your question but I think you’re trying to create something like the image below. Correct? If that’s the case you would create the menu structure either using the “Customize” or the “Menu” option in the “Appearance” menu in WordPress. The you simply arrange menu items the way you want them … Read more

Output existing wp_nav_menu with a custom walker

By default wp_nav_menu() outputs the navigation markup. If you want to store it or want to concatenate it with other string then you’d have to set the echo parameter to false (by default it’s true). $output .= ‘<ul class=”sub-menu”> ‘ . wp_nav_menu( array( ‘theme_location’ => ‘col_1’, ‘menu_id’ => ‘col_1’, ‘menu_class’ => ‘col_1’, ‘container’ => ”, … Read more

Next / Previous post in a single category

You can use the combination of in_same_term and excluded_terms. First of all, you have the ID of the category you want to display post from. Next, get all the id of the category of the post by using wp_get_post_terms You can iterate through the returned terms and build an array of terms that you want … Read more