In Fedora Server 38 and Fedora KDE 38 installer, it appears the only reserved usernames are: root, bin, daemon, and system. If you attempt using any other system usernames, e.g. "operator", the installer will silently fail to create a user account and create a softlock upon first boot. 

Fedora Workstation 38 does not seem to have this problem, likely because you create the user after install and has checks against existing accounts. I have not tested against other editions.

While it's unlikely the average user would create an account with a username like "lp", "abrt", or "dbus", there are some that an average user might try using. Hopefully there is a simple way to make it more average user proof.

Reproducible: Always

Steps to Reproduce:
1. Load Fedora Server 38 or Fedora KDE 38 Installer
2. Configure user account option to use a system reserved username other than "root", "bin", "daemon", or "system" (e.g. "mail", "nobody", "operator", "ftp")
3. Continue the installer normally, no errors should be reported
4. Reboot into new operating system
5. Attempt to log in with configured user account
Actual Results:  
Installer does not stop the use of username
User account does not exist on new installation

Expected Results:  
Installer stops use of system username