https://imgur.com/Hq5Txm0.png
Subpixel rendering is still 'enabled' in the defaults system:
~ % defaults read -g CGFontRenderingFontSmoothingDisabled
0
Perhaps there is some new defaults string in Catalina that can be set? It seems like CGFontRenderingFontSmoothingDisabled set to 0 still has some effect on Catalina, but it's not subjectively the same result as was the case on Mojave.