Hello, @Sara !
You may find that some VM sizes are unavailable as there is currently high demand for VMs in certain regions (this is especially true for free account VM sizes). The solution is to create your VM resources in neighboring regions during these periods of high demand.
In addition, we are in the process of adding new datacenters:
Our cloud is growing fast, and we’ll be adding 50 to 100 new datacenters each year for the foreseeable future to the 200 plus datacenters we currently have in operation across 34 countries. More regions were announced last year than any time previously.
When will my VM size become available again in my region?
Ensuring capacity for our customers is a top priority for Microsoft and we are working around the clock to deliver on this. The increasing demand for Azure services is evidence of the popularity of Azure, and emphasizes the need to scale up our infrastructure even more rapidly. With that in mind, we are expediting expansion and are improving our resource deployment process to respond to this strong customer demand. We have identified several improvements on how we load-balance under a high resource usage situation, and how to trigger the timely deployment of needed resources. Furthermore, we are increasing our capacity significantly – and will continue to plan for strong customer demand across all of our regions. This September 2021 blog post covers improvements towards delivering a resilient cloud supply chain.