How to turn off Nebula management？

Zyxel_JoyLee

To turn off Nebula management, you need to remove the device from your Nebula organization。
This can be done through the Nebula Control Center (NCC) web portal or the Nebula Mobile App.
Once removed, the device will reboot into standalone mode and revert to its factory configuration.
You can then disable Nebula Control Center Discovery on the device's web interface to prevent it from automatically reconnecting to Nebula.

You could navigate to CONFIGURATION > Network > NCC Discovery > Nebula Control Center Discovery Setting

Uncheck "Enable" check box and then click "Apply" button