Monitor or log dropped network traffic for Kubernetes NetworkPolicy
AFAIU, there is no way to create such vendor-neutral tool because NetworkPolicy is just an abstraction. Each networking plugin enforces them differently, (Cilium does that mostly in BPF for L3 and L4 and Envoy for L7), so each plugin needs to provide its own means of accessing this information.
AFAIK, there is no initiative in Kubernetes community to store this information and provide an interface for CNI plugins to provide this information, but it seems like it would be a fun project.
Disclaimer: I am on Cilium dev team.