Is it an IDP or K8s emulator like minikube?

Yup, Garden would be a tool that can help you build your IDP; https://docs.garden.io/use-cases/jumpstart-idp You basically use Garden to build this platform that developers can reuse to run miroservices in a Kubernetes environment, either local or in remote clusters.

Is it Internal Developer Platform or Internal Developer Portal?

Internal Developer Platform! This page is a good intro; https://garden.io/developer-platform

thanks