Ideally Disover should use systemctl soft-reboot, but nobody implemented that.
During Plasma 6 development, KDE switched to using systemd instead of kdeinit. Now when you start a session via a non-systemd init, you get a warning Falling back to extremely legacy forking mode. Yet they refuse to add support for soft-reboot for system updates. Either systemd should be supported with all its bells & whistles (already being done in Project Banana) or non-systemd support shouldn’t be extremely legacy.