To make NetworkManager in KDE works properly.
Stop the service first
# systemctl is-active network.service && \
# systemctl stop network.service
Enable NetworkManager
# systemctl --force enable NetworkManager.service
Enable the service again
# systemctl start network.service
Stop the service first
# systemctl is-active network.service && \
# systemctl stop network.service
Enable NetworkManager
# systemctl --force enable NetworkManager.service
Enable the service again
# systemctl start network.service