MariaDB offers tool to help understanding EXPLAIN output. It would be great to integrate something like this in phpMyAdmin.
Example:
https://mariadb.org/explain_analyzer/analyze/yucyd
Implemented with https://github.com/phpmyadmin/phpmyadmin/commit/ae4e5db3761ac0bbac9586c89ce956fae0b3f01f
Implemented with https://github.com/phpmyadmin/phpmyadmin/commit/ae4e5db3761ac0bbac9586c89ce956fae0b3f01f