I doubt LG will fix that. They will just call it a feature. Or it needs a true HDMI 2.1 source to go away, if not they would have fixed it already. Also I’m presuming the raised blacks is a feature to control Burn-in from Gaming.
My bet is that this is a simple oversight. Similarly to how the display panel behaves differently between SDR and HDR modes (higher W brightness ceiling, different ABL, etc), it also behaves differently between VRR and FRR modes. I guess they could make them look the same, either on the panel driver side or via the processor (for example, separate LUTs for VRR and FRR --- but if any Brightness setting causes elevated MLL, then it has to be fixed on the panel side, I guess). May be it's not even that (sort of mis-calibration) and only a simple bug (like a typo or trivial mistake in the code).