Client ≠ website. I don’t know what you’re referring to by “posting window” Respectfully, I have doubts you understand exactly where this censorship is possible above the client level.
Try it yourself, you won’t be able to post coercive language anywhere. It’s a general request made to make the internet a more decent place. There is no code involved.
What is an example of the coercive language you’re thinking of? I’m pretty confident I’ll be able to prove you wrong. Assuming we’re still on the topic of relays storing and distributing notes to other npubs.
Any swear word will do. Certainly it doesn’t matter if you try to post on Nostr clients where relays are storing and distributing notes or if you try any centralized app/website; you won’t be able to post any swear word.