I am using Red Hat Linux 9 and facing a strange issue with useradd.
When I am trying to add any user name with Capital letter name, it is
giving me error.

[root@nix3-rhel9 root]# useradd Abhirav
useradd: invalid user name 'Abhirav'
[root@nix3-rhel9 root]# useradd abhirav

the same command is working fine in RHL 8.

Any help would be greatly appreciated.