I do not understand this question.
Are you asking “is there zypper option for performing offline update”? No, there is not.
Are you asking “is it possible to implement offline update using zypper command”? Yes, it is possible. Just read the systemd documentation you mentioned so many times which describes how to do it using any program. Use zypper install --download-only to prepare update and create a service that will do zypper dup using downloaded packages.
If it means that pkcon does not ask you - offline updates are intended to be non-interactive, so it does not matter in practice.