Hi,
Thank you for posting your query. According to your description, I think these links can help you figure out your concern.
Using certificates in Remote Desktop Services
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn781533(v=ws.11)
Thin client RDS licensing
https://social.technet.microsoft.com/Forums/en-US/ac5d8cd6-a30e-4d6f-a5dd-6631b1461d8b/thin-client-rds-licensing?forum=winserverTS
Best Regards,
Grace
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