DecSync VS DecSync CC

A few years back I used to use SyncThing + DecSync for that purpose, and it worked quite well. Looks like it hasn't been updated in a while though.

https://github.com/39aldo39/DecSync

DecSync

There is decsync that works pretty good on Android. It stores contacts & calendars in a text file that can be synced with syncthing. There is a plugin for Evolution (Linux Mail client) but none for Thunderbird. But there is a plugin for Radicale, which is a caldav server. So you can run a local caldav server, connect Thunderbird to it and sync the decsync database with syncthing to your phone.

DecSync works with Syncthing to sync contacts and calendars.

I am a bit puzzled why so few people use DecSync and Syncthing for this?

I found some discussion here which is confusing when it says it wasn't designed to function this way when their own documentation seems to indicate otherwise.

I'm fine with either paying for software, or self-hosting something. If I go the self-host route, however, I would need to start and learn completely from square one. I saw some options in my searches that required software on my own server, but I wouldn't even know where to begin with that. DecSync came up in my searches, but based on the description I'm not sure if it would be linux only or not. (I'm on windows)

Afaik they use databases, and synching databases is bound to corrupt them. Generally you need a program to be aware that something can be accessing and even writing it's files at any time, as that requires special care (see e.g. for calendars and contacts: https://github.com/39aldo39/DecSyncCC). I'd look for an extension or something to export/import that data to files, which you then can use together with syncthing for a semi-manual process.

I have experienced this issue: https://github.com/39aldo39/DecSyncCC/issues/83

There are android versions of Syncthing and decsync on Fdroid or Google Play. IMO the only downside is, there is only a native plugin for Evolution. There is a plugin for radicale, which is a Caldav/Carddav server. So you can locally run radicale with decsync plugin, sync decsync via Syncrhing and sync Thunderbird, etc via radicale. This is still what you are looking for, but it is a little complex setup imo...

I have Tasks.org + DecSyncCC for android, with Radicale Server + Thunderbird for the desktop.

In alternative you can use DecSync CC, serverless sync with multiple devices using Syncthing (or other sync) https://github.com/39aldo39/DecSyncCC

DecSync CC (version 2.0.1): Sync contacts, calendars and tasks without a server using DecSync

I'm not sure I understand correctly, but take a look at this: https://github.com/39aldo39/DecSyncCC

Have you tried DecsyncCC? It creates a CardDAV and CalDAV account on your phone to synchronize your contacts, calendar, and tasks to a local directory.