I am perfectly aware of the Kubernetes API and that a manifest can be broken down in several K8S API calls.
I am wondering if there is a way to apply a whole manifest at once in a single API call. A REST equivalent to kubectl apply.
The feature is still in alpha but yes, it's called "server-side apply". Given the in-flux nature of alpha APIs, you should definitely check the KEPs before using it, but it's a new mode for the PATCH method on objects.