I am in a KDE for the moment and on my home pc other members of my family are using it. I have just moved to Kubuntu and when somebody else wanted to login got an invalid password error. actually,Digging I found that the even if the selected user was displayed correctly in the back it was the last user (mine) actually.
It seems that is a bug and until will be fixed on official channels here is the fix:
QML=/usr/lib/x86_64-linux-gnu/qt6/qml/org/kde/breeze/components
sudo cp -an "$QML/UserList.qml" "$QML/UserList.qml.bak"
sudo cp -an "$QML/qmldir" "$QML/qmldir.bak"
sudo sed -i \
's/(currentItem as UserDelegate)\.userName/currentItem.userName/' \
"$QML/UserList.qml"
sudo sed -i \
'\|^prefer :/qt/qml/org/kde/breeze/components/$|d' \
"$QML/qmldir"sudo reboot
