plesk version

As the title says, I am blocked on Plesk Obsidian 18.0.40, dated dec 2021 ! The only upgrade Plesk proposes is to 18.0.44, which fails : "There is no product aailable for your OS 'Debian' 'Linux' '9.13' 'x86_64' . I am stuck here, with old versions of php and MariaDB. Why ? How can I move...