Jason

This plugin solves the problem of when you have long pages/posts/custom posts edit screens in the WordPress admin, usually caused by lots of custom fields or plugins. Whenever you get down to the bottom of the page you need to scroll back up to the top to press the update or publish button. This plugin solves this problem by automatically scrolling the sidebar into view as you scroll the page.

Sticky Admin Sidebar

Simple, but very useful. Still works with WP 5.2 (you should SVN an update to the readme).

Still works

WordPress plugin to stick the post sidebar in wp-admin so it's always in view

Nazmul Sabuz

WP Stickit is a powerful WordPress plugin that makes any element on your website sticky with advanced customization options. Perfect for creating sticky headers, sidebars, navigation menus, or any other element you want to keep visible while users scroll.
Key Features: 
* Multiple Selectors: Use CSS selectors (classes, IDs) or separate multiple selectors with commas 
* Custom Positioning: Set custom top offset for precise sticky positioning 
* Z-Index Control: Manage layering with customizable z-index values 
* Responsive Design: Set minimum and maximum screen widths for responsive behavior 
* Lightweight: Uses the efficient jQuery Stickit library 
* Easy Setup: Simple admin interface with clear instructions

WP Stickit – Sticky Header, Menu, Sidebar & More

Make any element sticky with customizable positioning, responsive breakpoints, and z-index control.

Sticky Admin Sidebar vs WP Stickit – Sticky Header, Menu, Sidebar & More