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.

scribu

On the post editing screen, after saving a post, you will notice that the checked categories are displayed on top, breaking the category hierarchy. This plugin removes that “feature”.
Additionally, it automatically scrolls to the first checked category.
Works with custom taxonomies too.
Links: <a href="http://scribu.net/wordpress/category-checklist-tree" rel="nofollow ugc">Plugin News</a> | <a href="http://scribu.net" rel="nofollow ugc">Author’s Site</a>

Category Checklist Tree

Simple and without configuration, it's just does what it says it does.



Works as expected

Really, I just can't understand why WordPress developers walk another way - this is, how it should be! :)
I have launched over 100 websites on WordPress - and they all have this plugin.
Thanks again!

Thanks!

Preserves the category hierarchy on the post editing screen

WP Admin Category Search vs Category Checklist Tree