https://docs.microsoft.com/en-us/azure/container-instances/container-instances-multi-container-group
Below is a quote from the above URL.
Is there a technical reason that windows is not supported? Or will it eventually be supported? If yes, any idea when windows will be supported?
Multi-container groups are currently restricted to Linux containers. While we are working to bring all features to Windows containers, you can find current platform differences in Quotas and region availability for Azure Container Instances.