macOS need a dedicated download if you decide to use SSL VPN on those OS.
The article will always give you the latest available download, so you can follow this article, to get informed, when a new update is available.
Updates are usually the latest 4 weeks after a new macOS version is released available. Sometimes even faster, but always after the official release, to fine-tune the setup and version.
If you feel it takes too long, you are flexible to decide on another VPN type for macOS:
+++ You can buy licenses for your Zyxel VPN clients (SSL VPN, IPsec) with immediate delivery by 1-click: Zyxel Webstore +++