Mark Jaquith

This plugin increases the height of the category checklist meta box on the post editing screen so that all categories are shown. No more scrolling! All of your categories will be visible. If you’ve been frustrated by having to scroll to find the correct category, this plugin is for you. No options. Just install it and you’re good.

Category Checklist Expander

Increases the height of the category checklist meta box on the post editing screen so that all categories are shown.

scribu

newvibe

Must use Classic Editor plugin – Add to my list of gripes with Gutenberg that it uses the REST API to display the categories, adding nothing to the categories box for the user while rendering the wp_terms_checklist_args filter useless. If you don’t already use the Classic Editor plugin (installed more than 5 million times to date), you’ll have to use it for this plugin to work. I’m looking for a work-around…
Does your list of categories go on and on, making it difficult to scroll to and find what you need? This plugin will collapse groups of subcategories into expandable submenus, which you may open and close as needed, cutting your category list down to a manageable size. Submenus with checked categories are not collapsed (but are collapsible), so you won’t have to hunt for them.
Thanks to scribu for the code from his Category Checklist Tree plugin, which prevents the breaking of the category list heirarchy.
This plugin works with post categories and WooCommerce product categories too. According to users, it works with custom taxonomies!
Links: <a href="https://www.newvibewebdesign.com/collapsible-categories-in-admin-for-wordpress/" rel="nofollow ugc">Plugin News</a> | <a href="http://newvibewebdesign.com" rel="nofollow ugc">Author’s Site</a>

Collapsible Categories in the Dashboard

In the Dashboard, collapses sub categories into hidden submenus that can be expanded and collapsed.  Keeps selected categories visible.

Category Checklist Expander vs Collapsible Categories in the Dashboard