Where can I find and download the latest firmware for the AP?

Zyxel_JoyLee

You can download the latest firmware for your Zyxel device from the official Zyxel website.

The official download page for Zyxel firmware can vary depending on the specific product.

For example, the link for the NWA1123-AC PRO as:

https://www.zyxel.com/global/en/support/download?model=nwa1123-ac-pro

For controller-managed APs running firmware earlier than V7.10,an intermediate upgrade to V7.10 is required before upgrading to the latest version.

This is due to changes in the AP firmware encryption mechanism introduced in V7.10 to enhance system security and maintain firmware integrity. 

https://community.zyxel.com/en/discussion/33539/required-intermediate-firmware-upgrade-for-controller-managed-aps-running-version-earlier-than-v7-10

If your device is an End-of-Life (EOL) product, the availability of firmware depends on how long ago it reached EOL:

• If it's been less than 3 years since EOL, the latest firmware might still be available on the End of Life page of the Zyxel website.
• If it's been more than 3 years since EOL, firmware is generally no longer provided for these devices. You can check the Archived EOL Model list to see if your device falls into this category. For the best performance, security, and ongoing support, Zyxel recommends upgrading to a current Zyxel device.

https://community.zyxel.com/en/discussion/33255/how-to-download-firmware-for-an-end-of-life-eol-device