Philip Newcomer

This plugin makes all custom fields (post meta) visible in the “Custom Fields” meta box on post edit screens.

Show Hidden Post Meta

As a plugin developer, I create hidden post meta all the time and sometimes I need to see it to debug it. This does what it says it does, and well. Its simple and hasn't been updated for a while, but I'm glad it exists!

PS: If you need someone to take this one over, let me know. I'll keep it tested and updated if you're unable to.

Still works on 5.5

Makes hidden post meta visible on post edit screens

meloniq

Enhance the default WordPress admin search by including custom fields (post meta) in search results. 
This plugin seamlessly extends the post listing (edit.php) search functionality, allowing administrators to quickly find content based on values stored in custom fields.
It works out of the box with no configuration required—just activate and start searching. 
Especially useful for sites that rely heavily on custom fields, such as those built with ACF or other meta-based data structures.
Lightweight, efficient, and fully integrated with the native WordPress admin experience.

WP-Admin Search Post Meta

Search WordPress admin posts by custom fields (post meta) directly from the default search.

Show Hidden Post Meta vs WP-Admin Search Post Meta