Comment # 7 on bug 1050953 from Freek de Kruijf

freek@ltfctum:~> qdbus-qt5 --system --literal org.freedesktop.Accounts
/org/freedesktop/Accounts org.freedesktop.Accounts.CacheUser         
Error: org.freedesktop.DBus.Error.InvalidArgs
Berichttype ���()��� komt niet overeen met verwachte type ���(s)���
freek@ltfctum:~>

The command needs the parameter $USER and in that case starting systemsettings5
shows that user. The system prompts for the root password.

Just entering another username on the system also works and that user is shown
also.

However only the username and its full name, probably from /etc/password, are
shown. Tried to set an avatar. Setting it for a second user resulted in a
crash.

So apparently the system needs some initialization, like entering users in it.