My solution for to be able to use the latest DLSS in FS20 is, start FS20 and then the flight with TAA e.g. (restart FS20 with TAA if you close it with DLSS selected in options), both in 2D or VR, and then after the flight loads, change in options to DLSS, and after the flight change it again to TAA before close FS20, if not this workaround don´t functions (I guess with the other antialiasings work also, FXAA tested). Tested with DX11, HAGS off, and with any of the more recent Nvidia drivers, if that is related and helps.
Could you write here the strings to add or modify in the Registry to solve this to test?