One of my WB sites has more than 3,000 pages in 40+ categories. When I went to the pages section in the backend, it took forever to open. The pages in the front end were also slower. A few years ago someone here in the forum posted a solution for big sites which consisted in showing only the parent pages, and when clicking on the plus sign it would open a new page only with the second level pages, and so on. This made it a lot faster.
Problem is, after upgrading a dev version of the site from 2.8.3 to 2.12.1, this solution doesn't work anymore which is making the site horribly slow. I have been searching for the original post with the solution for doing this in WB 2.8.3 and I don't know if that specific code would work on 2.12.1 so I thought it would be better to ask for help.
In case it's of use, the site which is still on 2.8.3 (faster) is https://www.deguate.com
The test site already upgraded to 2.12.1 (slower) is https://www.superpromos.info/index.php
Thanks for the help you can provide!