Thank you guys for all your suggestions – so far I checked three of them (GSConnect is still on my list) with different outcomes:
Vdirsyncer
Unfortunately, I lacked the required knowledge and skills to understand the tutorial on http://vdirsyncer.pimutils.org and I could not find tips or even videos anywhere else. Someone very familiar with Vdirsyncer even advised me against using it since it was too cumbersome to use for the intended purpose. He instead recommended Nextcloud.
Syncthing
Is part of the repository and relatively easy to use -- I could set it up within a day. However, I could not find a way to synchronise calendar/contacts and if I did not miss anything, it's not possible without additionally using DecSync. Same problem as with Vdirsyncer: I could not find any info I could comprehend.
Nextcloud
Wonderfully easy to install and to get it to work. Calendar and Contacts on my desktop and on the Pinephone do indeed get the entries from Nextcloud, so it could potentially be the solution I was looking for. However, it does not work the other way around: The data from my desktop and from the pp does not show up in Nextcloud. Also, the entries from Nextcloud are not saved in the standard files (/home/mobian/.local/share/evolution/addressbook(or calendar)/system/contacts.db (or calendar.ics) and I have no Idea where they end up.
Is it possible to set up Nextcloud in such a way that it 1. actually synchronises Contacts and Calendar in both directions and (maybe less importantly) 2. saves the entries in contacts.db and calendar.ics?
Any ideas welcome … I don't want to give up at this point.
Vdirsyncer
Unfortunately, I lacked the required knowledge and skills to understand the tutorial on http://vdirsyncer.pimutils.org and I could not find tips or even videos anywhere else. Someone very familiar with Vdirsyncer even advised me against using it since it was too cumbersome to use for the intended purpose. He instead recommended Nextcloud.
Syncthing
Is part of the repository and relatively easy to use -- I could set it up within a day. However, I could not find a way to synchronise calendar/contacts and if I did not miss anything, it's not possible without additionally using DecSync. Same problem as with Vdirsyncer: I could not find any info I could comprehend.
Nextcloud
Wonderfully easy to install and to get it to work. Calendar and Contacts on my desktop and on the Pinephone do indeed get the entries from Nextcloud, so it could potentially be the solution I was looking for. However, it does not work the other way around: The data from my desktop and from the pp does not show up in Nextcloud. Also, the entries from Nextcloud are not saved in the standard files (/home/mobian/.local/share/evolution/addressbook(or calendar)/system/contacts.db (or calendar.ics) and I have no Idea where they end up.
Is it possible to set up Nextcloud in such a way that it 1. actually synchronises Contacts and Calendar in both directions and (maybe less importantly) 2. saves the entries in contacts.db and calendar.ics?
Any ideas welcome … I don't want to give up at this point.