zackdesign

Turn your WordPress post categories into a search powerhouse! This plugin gives you a set of dropdown menus based on parent categories and their sub-categories. Users select one sub-category per parent, and the plugin filters posts matching the selected combination.
Available as:
<ul>
<li>Gutenberg Block — “Multi-Category Filter” in the block inserter (new in v4)</li>
<li>Classic Widget — “Multi-Category Selection” in Appearance > Widgets</li>
<li>Shortcode — <code>[mcsw]</code> on any page or post</li>
</ul>
Features:
<ul>
<li>AND / OR category filtering — find posts matching ALL or ANY selected categories</li>
<li>AJAX chained drilldown — selecting a parent dynamically loads its children</li>
<li>Pretty permalink URLs (<code>/categories/3,5/search_type/and/order/title/</code>)</li>
<li>Ordering by title or default</li>
<li>Configurable blank search behavior</li>
<li>Exclude specific categories</li>
<li>Lightweight — no jQuery, no external dependencies</li>
<li>Pagination support</li>
<li>Display form above results on category pages (optional)</li>
</ul>
Sample use case:
Real estate — set up parent categories like “Bedrooms”, “Bathrooms”, “Price Range” with sub-categories beneath them. Users filter listings by selecting from each dropdown.
Upgrading from v3.x:
<ul>
<li>PHP sessions have been removed entirely — the URL now carries all state, which means better compatibility with caching plugins, load balancers, and modern hosting</li>
<li>jQuery has been replaced with vanilla JavaScript</li>
<li>CSS classes have changed from <code>wpmcsw</code>/<code>wpmm</code> to BEM-style <code>mcsw-*</code> classes — update any custom CSS</li>
<li>The old <code>select-chain.js</code> in the plugin root has been replaced by <code>js/select-chain.js</code></li>
</ul>

Multiple Category Selection Widget

Filter posts by selecting multiple categories using dropdown menus. Available as a widget, block, or shortcode.

Jam Viet

Your website sometime has many category and subcategory, it’s okey if Category has 2 sub category, but it’s will be bad if category has more than 3 children, this simple plugin will help you shorten all of them to a nicer permalink.
A permalink with a depth of more than 3 levels doesn’t look too user friendly. Additionally, Google may not worry much about URL depths, though it may impact searches on other engines like Bing or Yahoo. This plugin help you shortening deep subcategory’s link !
Eg: 
 //domain.com/category-parent/subcategory/subofsubcategory/last-subcategory.html 
Now it’s will be: 
 //domain.com/nameof-the-category.html
You can choose the end of the Url, can be html or htm or something like “.jam” is okey !
This plugin work with Yoast SEO also, no worry about anythings !
After active this plugin, you have to go to Admin > Setting > Permalinks to set-up suffix for Category link, or plugin will do nothing, suffix can be anything, eg: “.html” or “.asp” or even “.amazon”
Now the best way to setting main custom structure is “/%postname%” without the ‘/’ at the ending of URL, so the category’s link after shorten will have no slash at the end.

Shorten Sub-category's Link

This plugin help you shorten subcategory's link if it's too long or deep levels, help you boosting your SEO

Multiple Category Selection Widget vs Shorten Sub-category's Link