Recently I was upgrading a Drupal installation to version 9.5.11 and when in maintenance mode, received the error:
10.5.20-MariaDB-cll-lve-log
The libmysqlclient driver version 3.1.21 is less than the minimum required version. Upgrade to libmysqlclient version 5.5.3 or up, or alternatively switch mysql drivers to MySQLnd version 5.0.9 or up.
Since this installation was on a shared hosting account, I have limited control over the software version. I could switch to the MySQLnd driver. The MySQL native driver for PHP (mysqlnd) is a drop-in replacement for the MySQL Client Library (libmysql) for the PHP script language.
To make the change in cPanel, find the “Select PHP Version” in the Software section and click to select. In the “PHP Extension” tab make the following changes.
After doing this you should be able to continue your Drupal upgrade with no error.