Hello,
Based on my understanding, it is not possible to upgrade from Windows Server 2012 R2 Standard Edition to the Essentials edition of any Windows Server version.
There are only two approaches:
"When you upgrade from a previous version to a new version, the default is to retain the existing operating system edition. For example, the default is to upgrade from Standard (previous version) to Standard (new version), from Datacenter (previous version) to Datacenter (new version), or from Datacenter: Azure Edition (previous version) to Datacenter: Azure Edition (new version).
Alternatively, you can change to certain other editions when upgrading. You can change from Standard to Datacenter or to Datacenter: Azure Edition, or change from Datacenter to Datacenter: Azure Edition. You can't change from Datacenter to Standard edition or from Datacenter: Azure Edition to either Standard or Datacenter editions when upgrading."(see Upgrade and conversion options for Windows Server | Microsoft Learn)
The main editions of Windows Server 2025 will be Standard and Datacenter. Ther Essentials edition release date is not yet known. Microsoft recommend Microsoft 365 for small business customers as a replacement for all versions of Windows Server Essentials.
Regarding the license, I believe it is similar to the 2022 edition, being available only through OEM channels.
I hope this information helps.
Best regards,
Karlie Weng