After upgrading MySQL 5.7 to 8.0, it will not start, and an error similar to the following can be found in the MySQL error log.
Apr 18 01:34:47 server.domain.tld mysqld: 2023-04-18T05:34:47.360706Z 0 [ERROR] [MY-010022] [Server] Failed to Populate DD tables.
This issue usually occurs when a MySQL upgrade is attempted, and database changes are not compatible with MySQL 8.0
Please note that the MySQL Upgrade Checker utility should be run and all issues corrected before attempting an upgrade.
MySQL will have to be restored using MySQL dumps from the previous version after reinitializing MySQL.
Please note that reinitializing MySQL will result in data loss. Due to these risks, this process must be handled by a qualified system administrator. Downgrading MySQL/MariaDB may be possible however, there is no supported way to handle this in the cPanel software, and must be done manually by the server administrator.