In the online help, i's possible to directly upgrade from 11.20 to v 12 and onward, not including the step to upgrade to the same version before migration.
For more information, see the Qlik Online Help
Upgrade QlikView Server to a different machine:
If you are upgrading from QlikView 11.20 to November 2017 or later and choose digital certificates, there is no need to backup and restore your old certificates. New certificates are generated and installed automatically the first time you start the QlikView Management Service.
- On your current machine, create a backup of your QlikView Server 11.20 installation. See Backup and upgrade preparation.
- On the target machine, download the latest version of QlikView Server from www.qlik.com.
- Launch the QlikView Server upgrade wizard, and follow the on screen instructions. For a step-by-step description of the installation procedure, see: Installing QlikView Server.
- During the installation, select a service authentication method. Choose either Use digital certificates or Use QlikView Administrators Group. If you previously used digital certificates then you should also choose this option when you upgrade.
- Restart your machine once the installation process has finished to ensure that all services start up correctly.
- Open the QlikView Management Console, and apply your license information for QlikView Server, and QlikViewPublisher.
- You will be prompted to restart the server after applying the license information.
It's not necessary to upgrade on the current machine. Direct upgrade and migration is supported.