For local-first to succeed as a concept, it would gain a lot from having a Rails equivalent that people can get started on. If that exists, promote just that and hide all the other options.
Multi-master systems - which you have if the same data is being written to by multiple devices - are complicated, and there's no one size fits all solution. The different approaches all have different trade offs.
A good place to start might be "what do I think should happen when two bits of data that were updated independently are merged?".
Unfortunately we are far from having a go to platform. The community page's primary objective is to get the word out and connect local first builders.
I guess the answer is that JS/TS has never had a stack comparable to those py/rb behemoths.
back in the day, we built a real-time sports stats app on top of rails and firebase (before it was gobbled up by google) that provided some affordances in that regard, but truly offline first--saving locally, then syncing when online--would be a great rails use case.