Not a kubernetes expert, but my understanding is that that operators are regular programs that run in a kubernetes container and interact with the kubernetes AP

Not a kubernetes expert, but my understanding is that that operators are regular programs that run in a kubernetes container and interact with the kubernetes API to launch/manage other containers and custom kubernetes resources. An operator (or its custom resource) can be configured by Kubernetes YAML/API and its upto the creator of the operator to specify the kind of configuration. If the operator creator did not specify options to set cpu/memory limits on the pods managed by the operator, then you can't do anything. You have to add that feature into the operator and then make a pull request and wait for it to be upstreamed. Or fork it instead. Same thing for helm charts (except forking and patching them is easier than forking an operator).