If a ModuleScript object is has its Name property set to ‘MainModule’ and is uploaded to Roblox as a model to your account, Scripts can use require with the uploaded model’s AssetId instead. This allows you to create private modules on your Roblox account!
According to the post in the Private Modules announcement, private modules have been shutdown, source:
It’s not entirely wrong though. You can’t require third party private modules. You are still able to require private modules that you create and I believe also those that you own. In this regard, private modules aren’t shut down.
At the very least, a warning that third party private modules can’t be required would be appreciated, but I don’t think this paragraph needs to be removed.