YOOtheme Pro comes with great template for Joomla 404 error page. This Custom Element is specifically created to be a helper on these templates. The JP CE 404 Helper searches (from error URL) similar pages on your sites (or shows most popular if no results).
This plugin is a "Custom Element" and its very easy to add to the 404 page. To create a edit the 404 page create a external URL link to a "bad missing URL" (External URL menu item to yoursite.com/blablabla) and then you can create a 404 error Template page from within YOOtheme Pro (Templates).
Desing this page as you like and add the JP CE 404 Helper in the bottom (or where you see it fit).
You can see a demo here: https://joomlaproffs.se/uppgradera-webb