Sadly at the moment the Nostr protocol is not yet mature enough to do this on the relay side. I have tried suggesting proposals to do it but the developers consider it a low-priority optimization (yet integrating with Bitcoin Lightning Network is mission critical 🙄)
Discussion
I don't understand why it's not possible to hide or block an account? How is blocking an npub related to the relay?
I don't know what client you are using, but it is possible to block pubkeys on the client side. Unfortunately the client will still download all the events for your blocked pubkeys from the relay, which is inefficient and costly.
In addition, the client I use (Iris) has plenty of bugs in this area and still often displays events with pubkeys that I have blocked.
Amethyst at the moment, yeah that's what I was aware of the option to block is there but the content will still show and I don't want to flag is as scam all the time