Using syncthing to sync contacts, calendar and tasks without decsync, is it possible? Are there alternatives to decsyncCC?
It’s a bit complicated but there is way utilising Radicale (https://radicale.org). You basically run it locally, and then sync the whole Radicale folder between your devices (and I’d recommend to add the cache folders to ignore patterns in Syncthing because it does create a lot of those).
On Android, you can use Termux (https://termux.dev) to install Python and Radicale with it, and then use DAVx⁵ (https://davx5.com/tested-with/radicale) to make the Radicale data available to the phone apps.
I actually do my sync this way, as I used to have a lot of problems and errors with DecSync in the past.