@Hugo Le Guern
Hi,
Yes, he need to purchase a 2019 Standard license, Server 2012 R2 and 2019 are different versions.
Pricing and licensing for Windows Server 2019
https://www.microsoft.com/en-us/windows-server/pricing
You can refer to the following guide to upgrade from Windows Server 2012 R2 Standard to 2019 Standard:
https://learn.microsoft.com/en-us/windows-server/upgrade/upgrade-2012r2-to-2019
Hope above information can help you.
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