@Sheryar Apologies for the delay in response and all the inconvenience caused because of the issue.
I believe there is no RDS CAL involved in a 1:1 W10 user scenario via RDGateway.
As mentioned here
Remote access. No more than once every 90 days, you may designate a single user who physically uses the licensed device as the licensed user. The licensed user may access the licensed device from another device using remote access technologies. Other users, at different times, may access the licensed device from another device using remote access technologies, but only on devices separately licensed to run the same or higher edition of this software.
This document only lists SA and VDA as a requirement for Virtual OSE's , and i believe in this case its not a virtual OSE, instead a physical device running W10 locally, hence no SA/VDA requirement to my understanding
Hope it helps!!!
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