Petition the KDE maintainers to make it work like all the other KDE Background Services, rather than the ridiculous current approach of launching it at session start (whether the user wants it or not) and allowing systemd to automatically re-launch it (also against the user's wishes).
I want to test converting some noncritical but annoying services to systemd services. Then I will experiment with changing all to systemd services in a VM.
But if there is some strange systemd action in there that relaunches things, this needs to be adapted too.
I suspect @mox is confused somehow - as far as I know, KDEConnect does not provide any system service interface so systemd can handle it. It all happens in the KDE user session.
I know this because I don't use systemd and have KDEConnect working and autolaunching here.