Once a message is sent to relays, that’s it. Like nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s said, you can request deletion but your note exists on multiple independent relays and you can’t guarantee that every relay runner will comply with your request.

With Twitter or gmail, you are trusting that they delete the post, but 🤷‍♂️

I suppose it would be possible to only write to relays you trust to comply with deletion.