One per App Service Plan: The feature supports only one virtual interface per worker. One virtual interface per worker means one regional virtual network integration per App Service plan. All the apps in the same App Service plan can only use the same virtual network integration to a specific subnet. If you need an app to connect to another virtual network or another subnet in the same virtual network, you need to create another App Service plan. The virtual interface used isn't a resource that customers have direct access to.
https://docs.microsoft.com/en-us/azure/app-service/overview-vnet-integration#how-regional- virtual-network-integration-works