I think you've answered your own question below when you said about unplugging from the matrix. That means you are in the real world. Bitcoin is technically illegal now in the sense that it's not legal tender, and yet that doesn't prevent you and another person from agreeing to transact in Bitcoin. Same thing with Nostr, if it's illegal, it will be up to people to just decide to use it anyway, but for ethically sound reasons that don't break anything morally enforceable laws. If enough people do that, an illegitimate government which had made that protocol illegal would crumble in days. And that's why they won't ban it, because they know the ban would weaken them.

They can ban X in Brazil because they know it doesn't weaken them. X isn't a protocol, it's a platform, so it's not morally neutral. Banning Bitcoin and Nostr wouldn't be like banning X.