I followed the instructions on this page. Go yell at @Umbrel ☂️ if their documentation is inaccurate: “Connect your Nostr client (e.g., Damus, Amethyst) to your private relay for seamless backup of all Nostr activity. In Damus, add your Relay URL via Menu > Relays.”

Nostr Relay | Umbrel App Store

Discover Nostr Relay for your umbrelOS home server. Learn more, see screenshots, and discover other self-hosted Social apps available for umbrelOS.