Mark Jaquith

<ol>
<li>Check a category.</li>
<li>Uncheck “Uncategorized”.</li>
<li>Mutter “stupid ‘Uncategorized'” under your breath.</li>
</ol>
Sound familiar? With this stupidly simple plugin, you just have to do the first step. When you check a category and the default category was the only thing checked before you clicked, it’ll uncheck the default category for you. Boom.

Categorized

Unchecks the default post category when you first select a non-default category

Maria Daniel Deepak

WP Categories Metabox Extended extends the Category metabox on your WordPress editor. Once installed the Category metabox gets a search bar with which you search Categories. Also, this is only seen on “Add New Post” screen in the WordPress Admin dashboard.
From <a href="https://wordpress.org/support/wordpress-version/version-5-0/" rel="ugc">WordPress 5.0</a>, the search bar is included with the Categories metabox. In case you choose to use the Classic editor by using plugins like <a href="https://wordpress.org/plugins/disable-gutenberg/" rel="ugc">Disable Gutenberg</a>, then WP Categories Metabox Extended plugin will continue to extend the Categories metabox for the default “Post” post type.

WP Categories Metabox Extended

WP Categories Metabox Extended plugin allows you to search and assign Categories to your post in your WordPress editor.

Categorized vs WP Categories Metabox Extended