I think it's separate to subpixel anti-aliasing. It's whatever was controlled by the old "Use LCD font smoothing where available" in System Preferences > Genera

I think it's separate to subpixel anti-aliasing. It's whatever was controlled by the old "Use LCD font smoothing where available" in System Preferences > General. With that toggle gone, it can still be toggled using the "AppleFontSmoothing" defaults key.