What are the chances this could use an api to sync state with a server/service, for team usage?
Everything is saved locally on your Mac. You have full control over your data. No servers involved.
I'm somewhat of a control-freak when it comes to app data. For personal projects and data, I want an app that works offline and I want to know where my data is kept (preferably on the device).
Ideally I can even access my data in 10 - 20 years down the road, when the app doesn't exist anymore.
That's why each board is saved as single file on your Mac. You can see these files in Finder and even open them with a browser (they are just zipped HTML files).