You can not only set the PHP version individually for websites, but also use different versions of a database server for databases.
For example, you can test whether a certain page also works with a different version of the database server or you can use different versions because different websites work better with different versions of the database server.
To be able to use a different database version, you must first set up another version of the database server via the App Installer.
Once the installation is complete, you can change the database server of a database.
To do this, open the corresponding database under Websites. If you change the version of the database server, you may have to adjust the configuration of the website afterwards – however, most systems are updated automatically.