Synchronizing: How do you sync / synchronize Calendar and Contacts with your desktop?

[sfb]

Happy Easter holidays to all of you!

Is it possible to synchronise the calendar/contacts on the Pinephone with your Linux desktop?

The easiest way would of course be to connect the calendar/address book to an online account – but I do not want to give the data of my friends to Google or any other corporation just in order to move it from my phone to the laptop right next to it.

I have come across two possible solutions: I could set up a Nextbutt server (which is probably immensely complicated, way too complex for the tiny task intended and which may not work) or use KDEConnect (of which I don't even know whether it works on the Pinephone).

Is there any simple way to do it? The company Palm, which used to produce so-called palmtop computers, apparently had a small desktop program called "HotSync" that one could start on the desktop computer and it would synchronise calendar, contacts and files via bluetooth or cable. Is there anything equally comfortable for Linux? And if not: What would would the complicated solution look like?

I'm using https://ownyourbits.com/nextcloudpi/ on a raspberry (but it also runs on rock64) to do all the syncing, and this is one of the few things that work flawlessly with mobian. Takes less than a day to set up and takes trouble away for years.