Nostr: Can I delete a Nostr post everywhere?

Short answer

You can publish a NIP-09 deletion request for your own event. Supporting relays and clients may stop serving or showing it, but copies may already exist on other relays, clients, archives, or screenshots. Deletion is therefore a request, not a global recall. Avoid posting secrets or private information on the assumption that a later delete button will erase them.

Sources

NIP-09: Deletion requests.