How to choose display name vs nickname?

I don't think it is possible to choose.

But your real name and email address are only being displayed to you, because when you are logged in the forum software knows who you are and likes to show off. The rest of us see you as Starfox.

If you want to double check who can see what, click on the link in the upper left that says "Welcome [real name]" when you are logged in, and one of the options will be "Edit Profile". The other tab in the page it takes you to is "Privacy" which allows you to change who can see certain aspects of your profile, and preview what your profile looks like for other users or guests.

It's odd. I remember there being a privacy setting for displaying real name instead of username during the forum registration, but that doesn't appear to be a choice any longer.

There was an option in the settings for the old devforums.apple.com forums which allowed you to choose to display your real name instead of your username, but I don't think this new forum software has a similar option.

Almost as though the guy(s) responsible for such decisions read your post, the behaviour of this forum changed today (for me at least):

Now, no matter whether I'm logged in or not, I see the same as everyone else; my username only. The only place I now see my real name is if I view or edit my profile.

This should prevent exactly the confusion that prompted your post! 🙂