According to the privacy policy they only collect emails and usernames for your login methods. If you login with lightning they only collect the public key needed to verify your ln-auth

No, no IP addresses are stored.

Here is the database schema: https://github.com/stackernews/stacker.news/blob/master/prisma/schema.prisma

Not sure about logs though. IP addresses may appear there if they are not explicitly disabled.

But even then, you can't trust a service to have absolutely no information about your IP address since IP addresses are required for the internet to work. Hence the name: Internet protocol

So if you really don't want your IP exposed, use a proxy or VPN.

Curious about this as well.