This is perhaps more of a question for ACESCentral, but here is some info that may help you:

1)  MacOS uses ICC color management for the display.  OCIO is not integrated with that.  So to some extent, the answer to your question will depend on what the application does after calling OCIO.  For example, if the app is telling MacOS that it is an sRGB image, then you would want to use the ACES sRGB Output Transform and MacOS will try to make that look correct on the connected display via the ICC profile (even though it won't take advantage of the whole gamut).  Other apps bypass MacOS color management and so you should use the Output Transform that matches how the monitor is calibrated.  You may want to post on the forum for whatever app you are using for details along these lines.

2)  Apple uses P3 primaries with a D65 whitepoint.  ACES 1.0 had P3 Output Transforms with DCI and D60 whitepoints but ACES 1.1 introduced some addiitional P3 Output Transforms with a D65 whitepoint.  These would be closer to the Apple monitor.  However, all the P3 Output Transforms are intended for dark surround, whereas the sRGB Output Transforms (and Rec.709) are for dim surround.  Not sure which is more appropriate for how you are working, but keep in mind there is effectively a slight contrast and saturation difference between them.  If you want a P3 D65 dim surround Output Transform, that would be a request to make on ACESCentral.

best,

Doug

I am starting to adopt ACES1.0.3, and have a question about the iMac P3 displays. Most people seem to use ACES sRGB for viewing, but this is quite different from the display P3 color space. What display transform would be correct to use on an iMac?