How to "Optimize for" an external monitor, downscale resolution but supersample for clear text? I posted question here but got no answers --
https://discussions.apple.com/thread/8203211



ANSWER: 

Add a custom scaled resolution that's twice the resolution you want (for HiDPI / macOS retina). This requires editing system files.

STEPS:


Shut down Mac. Turn on Mac, holding CMD+R during bootloader, Utilities -> Terminal -> csrutil disable; reboot 





Login, download SwitchResX, install without helpers
Add a custom, scaled resolution 3200x1800 (looks good as 1600x900 HiDPI in 1440p)





Shut down Mac. Turn on Mac, holding CMD+R during bootloader, Utilities -> Terminal -> csrutil enable; reboot
I think you're misusing the term supersampling.


  Supersampling is a spatial anti-aliasing method, i.e. a method used to remove aliasing (jagged and pixelated edges, colloquially known as "jaggies") from images rendered in computer games or other computer programs that generate imagery.


macOS has always had support for TrueType, so any issues shouldn't be a result of poor antialiasing in any case.

What you really want to do is change the scaling of your external monitor while keeping the native resolution. You should be able to accomplish this using SwitchResX with a HiDPI profile.