What changes came into effect in April 2023 for Windows Server licensing?
As of April 2023, Microsoft has removed the requirement that a customer must have at least 16 Windows Server Core licences in their inventory before they can take advantage of virtual machine licensing or the Azure Hybrid Benefit.

In addition, a change to the Azure Hybrid Benefit came into effect where Windows Server Core licences no longer need to be held in groups of 8 when licensing a virtual machine with more than 8 cores. Previously, 24 Windows Server Core licences were required for a virtual machine with 20 cores (3×8), now only 20 licences are required.

Source: Microsoft Product Terms 2023-04