Steps to reproduce the issue

On SiteGround I am trying to install Joomla 4 Alpha 2, using Joomla_4.0.0-alpha2-Alpha-Full_Package.zip.

Expected result

After starting the installation, on getting to the Database Configuration screen, I would like to select a MySQLi database (but cannot), see screenshot.
After making a PostgreSQL database,
I want to specifiy

• host name,
• database name,
• database username
• password
• table prefix

Actual result

The only database option is PostgreSQL, no option for MySQL(i)
I only get the installation options

• host name,
• database username,
• password
• database table name
• table prefix
  (no database name).

System information (as much as possible)

PHP 7.2.1
database info from configuration.php that is created during installation (lines 14 to 20, edited for securitiy):
public $dbtype = 'postgresql';
public $host = 'localhost';
public $user = 'thomster_test4jo';
public $password = '[password edited out]';
public $db = 'thomster_joom4test';
public $dbprefix = 'mos6u_';
public $live_site = '';

Additional comments

location of installation: http://joomla4.tomhiemstra.nl/installation/index.php
screenshot: http://joomla4.tomhiemstra.nl/images/Werkblad_1_012.png