Privacyplease If a user finds a problem and reports it this makes graphene stronger.
I agree. This is why I'm spending so much time looking into this. I am not an expert on this stuff by any means, but as a fellow GrapheneOS user and a moderator I want to understand these things better. If I actually find something that concerns me I can assure you that I'd share my concerns.
Anyway, I've been trying to figure out more and I'm still not convinced it's a GrapheneOS issue. The site you're using is open source, so I found the code for it here. I've been trying to see how it finds your address, and as far as I can tell, there's no code attempting to get IP information from the OS via some API. Instead, it seems to attempt to use WebRTC to get this information. See this security note in the WebRTC docs for some related info. Here's most of it quoted here:
[...] the address property on RTCIceCandidate can expose more information about the source of the remote peer than the user expects. The IP address can be used to derive information about the remote device's location, network topology, and so forth. It can also be used for fingerprinting purposes.
The candidate IP addresses are always exposed to the application through address, and unsavory applications can in turn potentially reveal the address to the user. This can occur without the remote peer's consent.
Considering what's written there and the fact that you're expecting certain addresses to be private, I'd suggest using a VPN.
I have no idea why things changed on your end. I still can only get the nonpublic IP listing on Firefox and I'm not sure why that is either. I also can't explain why you get it using multiple browsers when I don't. But, still, I can't find or think of any way this can be caused by GrapheneOS or an update to the OS.
edit:
Privacyplease I just installed Brave and the behaviour is gone
Guess it makes sense to conclude that it's a browser thing, not an OS thing somehow. I'm going to change the thread's title and tags so other GrapheneOS users don't see this and think there's an issue with the OS without reason.