The "Display Name" field is where you can set it to your user + pronouns. I changed mine here to show you as an example. Using Jerboa btw.

There may be a character length limit to a Display Name which is what is preventing you from appending yours to your username.

I just tested it and putting test [he/him] as my display name worked fine. I'm using Liftoff though. maybe try doing it straight from the Beehaw site if you're doing it through an app?

I think you have to put them in your display name, alongside your actual display name.