If we are talking about a desktop client then I agree with you. However I have heard Nostr users claim that web clients also aren't subject to content regulations, but I don't think I buy that. I think websites are legally responsible for the content that they make available through embedding it in their web page.
Yes, TECHNICALLY the code that requests notes is Javascript that's being run in the user's browser, not on the Nostr web client's server, (at least that's the case for many Nostr web clients) and TECHNICALLY the notes are being sent directly to the client's IP address rather than to the Nostr web client's server IP. (Again, I'm talking about many Nostr web clients.)
However, the Nostr web clients are still the ones connecting users to relays and providing their browsers with the means to interpret that connection. And they are doing it all without verifying the age of the user. If the state has a problem with a website giving minors access to porn, they probably don't care much whether that porn is stored on the website's own server or someone else's. They don't care about HOW the website is giving minors access to porn, they only care THAT the website is granting minors access and that the URL at the top of the screen says you are on the same website.
