The latest advice is to set property vnetRouteAllEnabled to true instead of using WEBSITE_CONTENTOVERVNET as seen at:

https://learn.microsoft.com/en-us/azure/app-service/configure-vnet-integration-routing#configure-with-the-azure-cli

However, even that advice is not up to date, as that property has been renamed since Apr 2024:

az resource update --resource-group <group-name> --name <app-name> --resource-type "Microsoft.Web/sites" --set properties.outboundVnetRouting.contentShareTraffic=true --api-version 2025-03-01

See: https://learn.microsoft.com/en-us/azure/templates/microsoft.web/sites?pivots=deployment-language-bicep#:~:text=bool-,contentShareTraffic,-Enables%20accessing%20content