In short, I cannot find a suitable calendar application for my needs, for the following reasons
a) I need a calendar I can synchronize easily with several services outside google (memotoo, doodle)
b) lightning would theoretically work, but as can be seen easily in many fora, it slows down thunderbird to a degree that is unacceptable, even on a recent machine with lots of RAM
c) up to the last update, I quite happily used sunbird: it did all the right things, did not slow down my machine and was generally perfect - however since the upgrade to 12.3 it no longer works ("(crashreporter:10449): Gtk-CRITICAL **: IA__gtk_widget_set_sensitive: assertion `GTK_IS_WIDGET (widget)' failed" - I am unable to debug that)
Curiously, there seems to be absolutely no replacement. I have looked at evolution, but it wants to take over all of my life, and also does not seem to synchronize with memotoo. And kdepim seems equally huge and not promising at all.
Why could there not be a nice clean standalone thing such as sunbird was, and in fact still is?
Thanks for any suggestions!