As recently announced, Microsoft Defender Vulnerability Management (MDVM) add-on capabilities for servers are now included in the Defender for Servers P2 (DfS P2) license.
This means that any customer with a DfS P2 license will see MDVM add-on features light up in their tenant.
In other words, no trial was activated.
While the DfS P2 licensing is only related to servers, there is currently no granular filtering of machines, meaning that the capabilities are currently exposed for both clients and servers in the M365D portal. This is expected to be mitigated in the near future, in a way where a tenant with only DfS P2 licenses will be able to use the MDVM add-on capabilities just for servers.