With the launch of Drupal 9, one of the requirements is for MySQL 5.7 or later.
- If using Drupal 9 with MySQL or Percona, version 5.7.8+ is required.
- If using Drupal 9 with MariaDB, version 10.3.7+ is required.
What I discovered is the the version of MySQL that ships by default with Centos is constrained to 5.5*. To find my current version of MySQL:
$ mysql --version mysql Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1
I am also running Plesk control panel. Interestingly the latest available version of Plesk at the time of writing is Plesk Obsidian 18.0.30 that also supports MariaDB 10.3.7+ or MySQL 5.7.8+. Previous versions are constrained to 10.2.x
MariaDB 10.4 and 10.5 are supported starting from Plesk Obsidian 18.0.30. Previous versions (Onyx and older) do not support MariaDB starting from 10.3 and there are no plans to implement it currently.
Following these instructions I was able to upgrade my CentOS Box to the current stable version of MySQL (10.5.x). I can also now run Drupal Update without issue.
You may also need to lock your package from the Plesk admin UI to prevent Plesk from reverting to the default plesk version of MySQL/MariaDB under Tools and Settings > System Updates.