I'm curious on what you experienced that caused you to come to the conclusion that 3rd party sync solutions are not mature. There are several 3rd party vendors like Ditto that have been building local first sync solutions that are used by very large companies with success.
It’s a local-first platform that supports real-time sync with CRDTs at its core, making conflict resolution much easier to manage. Ditto is designed to handle offline-first use cases and peer-to-peer sync out of the box, so you don’t have to build a custom sync engine from scratch.
It supports a wide range of platforms including Swift, Kotlin (Android), Flutter/Dart, React Native, JavaScript (Web/Node), .NET (C#), C++, Java, and Rust. You can dive deeper into what it offers from the docs site:
https://docs.ditto.live/home/about-ditto
