Syncthing is an awesome tool.
In an attempt to use most open source software tools, I discovered that I like to have as much synchronization as possible in local storage (not on the internet).
Specifically have the laptop and the phone synchronized when they connect to the same network and regardless of the IP change.
One of the most difficult things is the contacts and calendars, for me between Linux and Android, which is only locally (not online) and that does not matter if the IP changes (sometimes I work at home, coffee, friends’ house, etc).
The only tool that works at the moment is DecSync CC that uses files that synchronize, for example using Syncthing.
Perhaps the negative is that it only works on Android and Evolution on Linux.
They can be used with other managers such as Thunderbird but adapting it with Radicale.
If someone has a better open source solution to synchronize contacts and calendars locally regardless of whether the IP changes please indicate it…