The available versions are 6.0 and 6.2. Earlier versions of Varnish are end of life at this point.
According to https://docs.acquia.com/acquia-cloud/arch/tech-platform/, Acquia is using Varnish 5.2.1 (which is end of life). Pantheon does not publicly list the version of Varnish it is using, but it used to be 4.1. As such, we'll need to decide what to do with the legacy versions.
There are now official Varnish Docker images available on Docker Hub: https://hub.docker.com/_/varnish
The available versions are 6.0 and 6.2. Earlier versions of Varnish are end of life at this point.
According to https://docs.acquia.com/acquia-cloud/arch/tech-platform/, Acquia is using Varnish 5.2.1 (which is end of life). Pantheon does not publicly list the version of Varnish it is using, but it used to be 4.1. As such, we'll need to decide what to do with the legacy versions.