You can talk in the physical world without being in any particular country so none of the governments have a monopoly either. With that definition we don't even

You can talk in the physical world without being in any particular country so none of the governments have a monopoly either. With that definition we don't even really need the concept of free speech as you always have a choice of where to speak. Social media sites have network effects and if you make your own site to put your speech on then nobody will ever see it. If you actually want to interact with others then you need to go on a big site that has a monopoly on the speech of that group of people. It's not that much different than a government and if we want to keep the concept of freedom of speech then we need to discuss whether those rights also apply in some way to public forums.