No matter how you like to participate in developer communities, Pulumi wants to meet you there. If you want to meet other Pulumi users to share use-cases and best practices, contribute code or documentation, see us at an event, or just tell a story about something cool you did with Pulumi, you are part of our community.

Pulumi Community

But then, ConfigFile resource is missing in preview, and, on successive executions, is deleted because mainfestUrl is not "Promise" anymore...

You can do `pulumi.output(rancherCluster.clusterRegistrationToken.manifestUrl).apply`
That will ensure that it is a `pulumi.Output`, even if its already available during preview.