It is possible to access a shared library over the internet from a DAAP client like iTunes. You must have remote access to the host machine.
First log in to the host and forward port 3689 to your local machine. You now need to broadcast the daap service to iTunes on your local machine. On macOS the command is:
ffid key is required but its value does not matter.
Your library will now appear as 'iTunesServer' in iTunes.
You can also access your library remotely using something like Zerotier. See this guide for details.
Accessing from Internet for authenticated users¶
If you intend to access Owntone directly from Internet, it's a good idea to protect it against unauthenticated users.
This guide has a detailed setup tutorial to achieve this securely.