The problem is not the implementation of Nostr, it is the IP protocol itself. It could have been designed without source address, but alas, we are stuck with it now.

You can spin up your own VPN, and then all your traffic will come from your VPN's VPS's unique IP, it won't be hidden in a crowd, like it would be with a commercial VPN. Tradeoffs, but that unique IP will get tied to you as soon as you sign into something, and then that IP is unmasked.

For nostr you can spin up your own relay, and have it download all your follows' notes. You can have that relay broadcast your notes to other relays, but those relays will see the IP you are broadcasting notes from, so if it is running at home, again your IP is leaked so you would want to run it from from a VPS or behind a VPN. Also I don't know what relays can be configured like I mentioned, out of the box.