Hi! Is there a way to wait for aws.route53.Record to be actually served ? Or, is there a generic ‘wait for an http endpoint to be present’ and pass it as dependsOn for another ressource?

That would depend on the resolver rather than the record, I think? If you're using a private zone, then any old dependency should work. If you're resolving via an external DNS service, then there's nothing built into Pulumi that you can use. But you have the full power of your preferred programming language, so you can wait on the end point to respond using your preferred HTTP client lib.