When you're choosing virtual sizes for your workloads, we recommend that you select from the current generation of virtual machine sizes and specifications. With a recent update to the virtual machine size picker, the default filter set will show current-generation virtual machine sizes only.
When you use the Compute type filter to find sizes that support particular workloads (compute optimized, memory optimized, etc.), you see the appropriate sizes in the current generation only. You can still find older virtual machine sizes by selecting Previous generation from the Compute type filter.
Learn more about Azure virtual machine sizes for Windows