Joomla 4 is >= php 7

http://php.net/manual/en/mysql.php

Depending on the version of PHP, there are either two or three PHP APIs for accessing the MySQL database. PHP 5 users can choose between the deprecated mysql extension, mysqli, or PDO_MySQL. PHP 7 removes the mysql extension, leaving only the latter two options.

Just a note, because of the Framework Database package structure, the $dbtype in the config will be "mysql" if using the MySQL PDO driver. Unless a merge went bad, the option should still be labeled in the UI as "MySQL (PDO)" (or something like that).

I meant MySQL (PDO). That is what is not working

In the installation process it is shown as MySQL and not as MySQL (PDO)

Edit: Ok, I found out why that is in this case. The "calculated" language is English (United States). This language file has not been updated yet to show MySQL (PDO) for the mysql value.

experiencing the same issue with PDO,
can someone help me to understand onTableBeforeReorder event stand for ???

Unable to replicate on current 4.0 branch when using pdo

I am closing this - it can always be reopened if required