On NOSTR, you can't stop someone seeing your posts by blocking them, you can only stop seeing their posts by blocking them.

If someone writes offensive content and you wish to ignore them, block them. Even their replies to you will be ignored.

If you want to write a private message, create a private group chat or private direct chat and message in private.

Even with twitter if someone blocked me but I wanted yo see their post, I would just load it in an incognito mode browser and I could see their post. Why try to make public posts and try to exclude one person?

Go private or go public. Don't try to abuse the platform to exclude individuals, but do use it to filter out unwanted spam, noise and unplesant content.