Currently PowerApps supports offline capabilities (SaveData, LoadData, Connection.Connected) only in Windows Desktop and Mobile Apps.
But currently Desktop app is significantly slower than Chrome.
Actually Desktop is event slower than running app on Android phone, I think this is because Desktop is powered with Edge engine.
It would be very helpful to implement support SaveData, LoadData, Connection.Connected for browsers.
I am sure this is very easy to implement this by saving and loading data to localStorage and check connection by window.navigator.onLine.
It is not clear why Microsoft haven't implemented this initially.