Hi,
If you want to deploy a [smalldisk] image in the Azure Portal, you should start in the Marketplace. Search for [smalldisk] and a list of available images will appear.
Looks like there's currently only one image available in the Azure marketplace:
If you're deploying Azure VMs with ARM templates, you can follow along here:
https://www.dynamicbatech.com/devops/azure-vm-images-with-smaller-system-disk
Best regards,
Leon