How to integrate Lightning Calendar (Thunderbird) with KDE?

I would like the KDE Calendar widget to display the calendar events from my egroupware calendar (Caldav) which I have configured in Lightning (This is no longer required in Thunderbird >=78). The server uses TLS client certificate authentication which is not supported in KOrganizer, even though well voted for respective bugs exist since 2006. Therefore, I cannot directly connect the calendar to KOrganizer.

PS: Kubuntu 21.10, Plasma 5.22.5, Thunderbird 91.5, but all this should be rather irrelevant

Update: I have managed to create an .ics file calendar in Lightning that is accessible to KDE. if someone tells me how to synchronize locally two calendars in lightning that would be a complete solution. Alternatively, if I could automate exporting from Lightning to an ics file (overwriting the old one), this would also be a complete solution.