This is not correct, you can of course preview images in different profiles on the Mac, including Adobe RGB. The latter only makes sense if the monitor you use supports 100 % (or very close to 100%) of Adobe RGB's color gamut. And you
could preview your photo in other color spaces (including Adobe RGB), although if you are not careful, the preview will look nothing like what other people see when you send them the photo.
The problem here will be most monitors do not cover the whole gamut of Adobe RGB colors. You mention that you use a Benq SW-series monitor, and
at least some models supposedly cover 99 % of Adobe RGB. I say supposedly, because the only way to know for sure is to create a color profile with a hardware calibration tool. Once you know that your monitor's gamut really does cover almost all of Adobe RGB does it make sense to preview files that use colors from the whole Adobe RGB spectrum with your computer/monitor combo. Few monitors really get close to being able to display Adobe RGB's color gamut, and Apple is aiming for 100 % coverage of DCI-P3. (DCI-P3 is a standard from the video industry, and it is being picked up by many other smartphone manufacturers.)
It is not clear to me what your problem is: we do understand the difference between calibrating a display and viewing photos after applying different output profiles. Insisting to use a profile that includes colors which your monitor cannot display makes no sense and is just asking for trouble. Are you changing the
display profile rather than the proofing profile?
You should keep your display profile fixed, preferably you should create one yourself with a hardware calibration tool. Don't muck with settings on the on-screen display after calibration, keep it as it is. The display should have a gamut wide enough to contain all of the colors supported in the proofing profile. If it doesn't, then it isn't good enough for this particular proofing target.
No, that is not correct, DCI-P3
overlaps 93.6 % with Adobe RGB and Adobe RGB overlaps with
87.0 % of DCI-P3.
Nice explanation. The only thing I would add is that there is a bit of variability when it comes to how colors are treated that lie outside of the color gamut that is displayable by the device (e. g. your printer or your monitor). But of course, the underlying fact that you are dealing with a representation does not change.
Yup. If you really care about color accuracy, you have to create versions of the image optimized for each type of output. There is no “true” colors, unless every device along the way treats profiles correctly and all devices are calibrated. If you want to print a photo, you need to know the printer/paper combo and optimize for that. If it is for the web, pick sRGB, etc.
From what I read here, it seems you don't understand how color management works: you only need to calibrate your monitor once. You definitely do not calibrate your monitor for different color spaces. When you get images from a device which has not been calibrated (like in almost all circumstances digital cameras), meaning if you take a photo of a reference color target
such as this one, the colors will appear differently on your monitor. That's why you can assign a color profile of your choosing in digital cameras. Of course, depending on what profile you choose (on digital cameras that is typically either sRGB or Adobe RGB) that will change the way an image is rendered, but it will not change the underlying data. In fact, if you shoot RAW, there is zero loss of data. As soon as you start working in a calibrated environment, you have to keep track of the color profile. That means if you edit the photo to “look just right” on your calibrated screen, then when you save your photo you need to include an output profile (e. g. Adobe RGB). If you then open it on another machine or printer whose color gamut is large enough to display all colors, it will look exactly the same way. As you noticed, the output profile can be different from your screen's or printer's profile.