At the time of asking there is zero useful information on https://developer.apple.com/documentation/imageio/kcgimagedestinationoptimizecolorforsharing?language=objc
In the header it says:
/* Create an image using a colorspace, that has is compatible with older devices
* The value should be kCFBooleanTrue or kCFBooleanFalse
* Defaults to kCFBooleanFalse = don't do any color conversion
*/
but isn't completely clear what is going on.
I note that sips also seems to support it with the incredibly unhelpful information on the manpage:
--optimizeColorForSharing
Optimize color for sharing.
Any details about what is really going on would be appreciated.