What exactly is "Project Network Isolation"? The reference manual for 2.7 (https://ranchermanager.docs.rancher.com/reference-guides/cluster-configuration/rancher-server-configuration/rke2-cluster-configuration#proje[…]ation) doesn't tell. Is it safe to enable this feature? What are the advantages and pitfalls? Every insightful comment is highly appreciated.

Project network isolation is used to enable or disable communication between pods in different projects. It basically creates network policies that prevent direct pod-to-pod communication in different projects. So if you have a pod in project A and a pod in Project B they won't be able to communicate directly.