STRATUS allow you to choose which version of Varnish you wish to employ on your Magento installation.
Magento 2.3.3+ supports Varnish version 6.
To change your version,
- Go to Varnish > Version in the STRATUS sidebar menu.
- Select the version of Varnish you wish to run.
- Click UPDATE to save changes.
NOTE: changing the version will cause a reboot of your installation.