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

Search field as a new tab. Click Go to go back to the filtered list.
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.