PHP 5.6 is missing from Plesk Installer.
Is it possible to install PHP 5.x in Plesk on Debian 9, 10 and Ubuntu 18, 20, 22 via Plesk Installer?
By default, these operating systems support only PHP 7.x compatible with OpenSSL 1.1. Also, PHP 5.x is outdated version.
Therefore, it is not possible to install PHP 5.x via Plesk Installer and we DO NOT recommend installing it manually as it may break web applications and compromise whole server security bringing them out of Plesk support scope.