The app that synchronizes multiple lemmy accounts so you can migrate and keep backup accounts across instances, it's opensource and free, currently working in android and windows.
It's in homologation now and anyone can test, any feedbacks are welcome as always.
How does this handle cases where no subscribers from an instance have subscribed to an external community yet? Other migration tools I have used require these to be added manually. Does yours automate this process?
Didn't get a chance to look at how your app works under the hood, but for LASIM I look up the community by name to get the ID and then call thr subscribe API. The former did seem to trigger the Lemmy instance to "learn" about the community, but it takes awhile, and there is no way to know when it has learned it other than to retry looking it up a few times.