Ok sorry for that.
Anyway I deleted the DisplayProductID-* that I created and downloaded RDM app. From there I can see multiple resolutions including with Lightning icon which I think are the HiDPI resolutions.
I just need some clarifications, first do I still need to create the override file (plist)? My monitor resolution is 3840x2160, so for me to get a true Retina (2x), I should choose a resolution which is (3840x2160) / 2 which is 1080p. Am I correct? And so 1440p HiDPI is not true Retina quality?
EDIT:
I've been reading previous pages of this post and noticed that most if not all are using the Intel graphics. I have the RX 460 GPU with the iGPU Intel HD630 enabled on BIOS. Could this be a reason of why my custom resolutions doesn't appear in Sys Pref?
I came across a question if it works on Nvidia cards but the answer was "I don't know".