When I go here https://itch.io/user/settings I find my email address in the "Display name" box (annotated as "Name to be shown in place of your username, leave blank to default to username").

I did not put it there. Turns out, this is a suggestion itch.io makes ... which would become public the moment I click "Save" at the bottom. This is a very easy mistake to make and clearly unintended by itch.io and definitely by the users.

If I enter a name here and save, that name is shown at the top of my profile. If I now remove that text and save, my profile shows the true user name again ... and the "Display name" box is again populated with the private email address. This is a serious issue.