ZERØ for Intune application is specifically designed for MDM deployment via Microsoft Intune. This app allows both ZERØ and Microsoft Intune customers to take advantage of a secure Intune MDM deployment, organize and protect BYOD environments with mobile application management (MAM).
If you do not intend to use ZERØ with Intune MDM then you can download the main ZERØ application here: https://apps.apple.com/us/app/zero-email-for-attorneys/id1216474378