Is it possible to save the kubeconfig to a file when running pulumi up?

I would typically do this by either getting the kubeconfig from the exported values, either via the CLI or via the Automation API (i.e. running the stack programmatically and then being able to access the exported values). I guess you could write out it in an

apply

block but that seems generally ill-advised

Yeah I just assign to an output and later read it using the cli and write a kubeconfig file for use by kubectl or k9s