Elasticsearch explicitly does not support upgrading from prerelease versions to GA:

This documentation is for a pre-release of Elasticsearch 8.0. Upgrades from pre-release builds are not supported and could result in errors or data loss. If you upgrade from a released version to a pre-release version for testing, discard the contents of the cluster when you are done. Do not attempt to upgrade to the final release.

The Kibana docs seem to imply that it's okay for Kibana, but we should not encourage people to treat the pre-release versions as a step on their upgrade path.

Additional changes will be needed as part of the upgrade doc refresh, but let's get this changed so we're not sending mixed messages in the interim.