Disabling public network access for Azure IoT Hub will disable access to built-in Azure Event Hub endpoint on September 30, 2020

When public network access to Azure IoT Hub is disabled, the built-in Azure Event Hub-compatible endpoint in IoT Hub may continue to be accessible via the public internet

On September 30, 2020, this behavior will change, and public access to the built-in endpoint will be disabled when public network access is disabled for IoT Hub.
Source: Azure Roadmap