With DirectWrite and Freetype, subpixel rendering isn't done for colored rendering. On OSX, due to lack of subpixel with Core Text, it also isn't done.
I suspect what you're really asking is "why does high color contrast look weird at the edges?" Because some monitors are "exceptionally clear and sharp", and people have been selecting monitors for this trait for over a decade.
On LCDs, "good" polarizers make it hard to make out individual subpixels (which also makes subpixel rendering kinda moot on them; you'll see the fringing but the text won't look any sharper than greyscale, and noticeably less sharper than aliased); instead of "clear and sharp" they're more "natural".
OLEDs and MicroLEDs do not have polarizers, and they're the sharpest monitors I've ever seen. However, good news (at least for me): I can see subpixels on a 1080p 24" during high color contrast (ie, fringing fonts), I _cannot_ see them on a 4k 24".
Even if I integer-scaled 1080p to 4k, I would be using an array that looks like...
R G B R G B
R G B R G B
.. to represent pixels. I can't see subpixels during situations like this. So, the only way to avoid the problem is just use HiDPI monitors. 32" 4k seems to be a very common size for Mac users; it causes it to do Retina scaling correctly, while also being about 150% the DPI of a 24" 1080p, or about 125% of the DPI of a 27" 1440p (the two most common sizes).
My recommendation also is: never use below 4k on OSX. OSX's handling of sub-4k monitors is broken, and usually leads to in-compositor scaling instead of letting apps natively render at LoDPI.
