Many people don’t upload photos while creating their user profiles. Is it possible to display real names or usernames instead of Avatars?
Avatars and Names are completely separate elements, so I’m not sure what you mean.
If a member has not added an image to their avatar / profile, then the system defaults to using a letter (the first letter of their username) in a coloured background to identify them, so that this relates, in a small way, to that user, so we are already doing what you are suggesting.
If you want to control the name on the site, then there is a related topic here:
Please do consider searching the resources on this site for lots more information
I started to use Sam’s Simple Theme. It displays the username of the post creator in posts list.