It was recently elaborated why FreeSync support over HDMI is not reaching open source drivers, at least not yet … This stems from the HDMI Forum’s decision to prevent public access to the HDMI specification, which in turn is hampering drivers open source graphics.
With the HDMI specification not being public anymore, but only for “HDMI Adopters” it is complicating the support of the open source GPU driver. Even for those who are part of the HDMI Forum, like AMD, for its part, it cannot provide an open source implementation of features covered by the closed specification to, in turn, potentially open and indirectly aspects of it to the public.
This situation appears to be the main blocker of why FreeSync with the open source AMDGPU Linux kernel driver works only with DisplayPort and not HDMI connections, which has persistently been a major issue regarding FreeSync Linux support and its current shortcomings .
Current restrictions on the HDMI specification put many advanced HDMI features at risk for models such as HDMI 2.1 from being implemented in open source graphics drivers.
The X.Org Foundation is asking the HDMI Forum to at least allow some HDMI 2.1 specification information to be made publicly available so that open source graphics drivers, in turn, can (legally) implement the functionality.
Hopefully it will work in 2021 … In the meantime, keep that in mind when deciding on DisplayPort vs. V preferences. HDMI!