There are updaters for all 3 platforms supported - Linux, Mac, Windows.
Those updaters don't contain the game engine! At least not at the moment. They update the game files with the new content through a process which can be run at the mentioned OS. So the macOS updater (patcher is a more correct term) updates the game files on a macOS. It will work if you have a previous downloaded Windows game. So ideally we are working to the following system to minimize the downloads:
Windows full => most people use Windows so it is logical that this contains the game files as well as the Windows engine
Windows patch => converts the previous Windows full (or patched version from an earlier full) to the newest version
macOS patch => converts the previous Windows full (or patched version from an earlier full) to the newest version
macOS engine => adds the platform specific game engine to the Windows full version (or patched version)
Linux patch => converts the previous Windows full (or patched version from an earlier full) to the newest version
Linux engine => adds the platform specific game engine to the Windows full version (or patched version)
Because we don't have the macOS engine yet Nenad is also exports a macOS full version at the moment. Because the engine files are small -- less than 50 MiB -- they could be added to the patch files for that OS as well. But that is work in progress at the moment...