Nostr supports a deletion event kind to request event removal (https://github.com/nostr-protocol/nips/blob/master/09.md)
Here is tool for that: https://delete.nostr.com/
But not all relays will respect that.
Users who are concerned about that should only pick relays that respect event delection.
I once saw a website that mentioned all popular relays and which NIPs they had, if someone has it please post. Or you can go 1-by-1 of your relays using this tool https://nostrrr.com and check if they have NIP-09 support.
The relay support for NIP does not guarantee execution. The only solution, but not advisable, was to have a personal relay and write only on it.
reply
If you are only using "write" on your own relay, then no one would be able to see your notes.
Other users would need to connect to your relay to see your notes. And no one will do that. Most people only run 10 relays on average, and mostly popular ones (top 15).
One of the key points of Nostr is to spread your notes across multiple relays, so if something happens to one of them, you don't lose anything.
reply
Let's say I only have one personal relay, and some people are already following me. Shouldn't people client connect to my relay?
reply
As far as I understand, when you follow or post notes, they are categorized as 'Events' and are disseminated to your relays.
This implies that if you have X relays that are completely distinct from those of another person, they would not be able to see your notes.
However, there are certain relays that automatically fetch data from other (popular) relays, and services that distribute your notes to all the popular relays on your behalf.
One issue with Nostr imo is the centralization problem of popular relays, as individuals will need to use at least a few highly popular relays to garantee that all their notes can be retrieved by all users.
Perhaps someone with greater familiarity with Nostr can provide additional insight, i'm still newbie.