Nostr: Can a relay censor my posts?

Short answer

A relay can reject, remove, or decline to show events on its own server. It cannot invalidate a correctly signed event that survives elsewhere, and you may publish to another willing relay. However, a widely used relay's policy can still reduce reach. Keep copies of important events and use suitable alternate relays; decentralization offers options, not a guarantee of audience.

Sources

NIP-01: Basic protocol, NIP-65: Relay lists.