atillaordog

The search fields simply filter the lists in their current box.
Use the settings page to manage the location of search fields.
Simple as the sun, using easy JS.
Especially useful when there are a lot of categories, like in case of a shop.
It needs jQuery to run ! 
Trims beginning and ending spaces ! 
Works with the classic editor of WordPress 5, the new editor has this functionality included.

WP Admin Category Search

The plugin works flawlessly and is very simple.

Works fine and solved my problem

This plugin adds search functionality to category-like taxonomies and dropdowns like author on add / edit post / page admin pages.

Marzio Carro

Adds categories and tags functionality for your pages.
This plugin addsthe ‘post_tag’ and the ‘category’ taxonomies, which are the names of the existing taxonomies used for tags and categories the Post type ‘page’.
This enables the categories metabox and the tags metabox in the New or Edit Page interface.
The plugin has no settings, does not alter the database and only uses hooks to 
achieve it’s goal. It works perfectly fine with Multisite installations.
This plugin WILL NOT add any display of categories or tags to your template files.
Plugin’s website: <a href="http://technotes.marziocarro.com/category/wordpress-plugins/" rel="nofollow ugc">http://technotes.marziocarro.com/category/wordpress-plugins/</a>
Author’s website: <a href="http://technotes.marziocarro.com/" rel="nofollow ugc">http://technotes.marziocarro.com/</a>

Category Tag Pages

Wonderful functionality

Yes, it works. Uses very few lines of code and it's a simple and safe solution to have categories and tags in pages.

It works

Adds categories and tags functionality for your pages.

WP Admin Category Search vs Category Tag Pages