It seems like the game must be restarted and re-attached to VorpX with every change I make to it’s settings, otherwise it will not take effect in VorpX.
So I must go through all the Antialiasing settings, Resoultion settings and Fullscreen/Windowed modes with restarting the game every time. As I understand, AA anti-aliasing are 3 things in RDR2: FXAA MSAA and TAA. FXAA has 2 options – On or Off; MSAA has 4 options – Off, X2, X4, X8; TAA has 3 options: Off, Medium and High. So will take some time.
If it helps GTA V with VorpX works flawlessly.