The versions we can test on are somewhat limited by what Amazon/Microsoft/Google have available, and they have historically lagged behind by a fair way. We also have in the past selected versions to certify based on whether all cloud providers support that version at the same time. We realize this isn’t optimal for users living on the bleeding edge, so we are committing to testing as far upstream as we can, regardless of other cloud providers, then continually updating our support matrix as new platforms become available. Things will get better, that I promise you!
As regards 1.18… it won’t work because of how Kubernetes Endponts are implemented now, however we will have full 1.18 support in Operator 2.1 (coming soon!)