What is the best way to design a generic clipboard?

Question

macOS

There are mac, pc, iphone, you need to create a universal clipboard between them.
Those. inserted text from pc/mac'a/iphone, posted it to the cloud, took it from other devices
In this regard, there are several questions about the correct implementation of this case.
Let's say there is a form with textview on a poppy, there is a callback to change the text

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.buffDidChange(_:)), name: "NSTextDidChangeNotification", object: nil)

But it works for every character, the text needs to be sent to the server either after a pause of several seconds, or after pressing the enter button
. not just a couple of characters typed, but then how to create a new thread with access to the textview?
What is the right thing to do from the side of Windows (c#) in this case?
How to properly design a web part to write to the database in only one thread?