I think the impressive part here isn't Linear's sync engine, but the fact that Evan Hu went through painstakingly reverse-engineer the engine by inspecting traffic and obfuscated code and was able to write documentation that is correct and more complete than what Linear publishes internally.
In comparison to the web where there's so many libraries e.g. Zero, LiveStore, LiveBlocks, I've yet to find a good GRDB (sqlite abstraction) integration / client.
Offline-first is definitely very strong, but now how do I get data into a remote database with conflict resolution support?