We are currently using Varnish 3 which has reached its end-of-life.
We wanted to upgrade to a newer version but when checking the release summary seems all new releases are shown as "retired"
Specifically: https://varnish-cache.org/releases/
Does "retired" mean it should not be used? And if so, which Version is the latest stable release.
Version 4.0 shows as end-of-life, but 4.1 shows as "supported", would this be the latest version for production use?
Varnish 5 was retired and should not be used in production. You can first upgrade your varnish config to 4.x and then use Varnish 6 in production with your 4.x config (it is supported in varnish 6)
Best regards