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:
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Design and visualisation for new B2B directory that utilsed the PHP Link Directory CMS.
Bespoke CMS system that allows authorised users to add, edit or delete information stored in a MySQL database.