Photoshop not showing correct colors. Update after 3 weeks of troubleshooting.

It is important to note that this issue is not related to the GPU in Mac computers. Rather, it is a specific problem with Adobe Photoshop.

By @TheBeatnikHimself

I demonstrated correct behavior, further up, on a Windows machine. It does not occur on Windows.

Today, I ran a few more tests. I noticed that the two monitors I use at work perform quite well in terms of "gamma" in sRGB mode, even without calibration.

Today, I went ahead and tested/calibrated both monitors (using a Windows machine).

As previously discussed, regardless of the TRC, when Color Management is enabled, the results should always be the same, and I confirmed this on windows machine thanks to @D Fosse .

Then, I compared results with crappy macOS.

When I calibrated to gamma 2.2, macOS freaked out. Blacks started appearing way too bright. If you're also using Photoshop ACE, it brightens them even more. The Lightroom Develop module looked almost fine with gamma 2.2, but there were still differences. Photoshop is not even usable.

However, I noticed something. I thought it would temporarily make things much easier for you @riccknl, so I wanted to share it with you.

We know that on Windows, regardless of the TRC (sRGB, gamma 2.2), you always get the same result.
If you're using DisplayCAL, you can select the TONE CURVE. Up until now, you might think it shouldn't make a difference. But thanks to macOS bugs, it actually does and that was/is our problem.

If you select "sRGB" as the TONE CURVE in DisplayCAL, you get almost the same result as on Windows!
RGB 1,1,1 values are nearly identical, and RGB 2,2,2 values are slightly/marginal bright on macOS, but the difference is really  small.

When you set the TRC to sRGB when calibration, macOS interferes less on the GPU side. (You don't see the brightness increase by another step one second after changing the profile when using Photoshop with ACE.)

Except for the Lightroom Library module! Other than that, I get the same results in Lightroom Develop, Photoshop, and macOS Preview.

This way, you can use Photoshop in "ACE" mode without issues, and the system doesn’t freak out—it works just like it does on Windows. Just remember, this doesn't apply to the Lightroom Library module.

But remember, this is not a fix, just a work arround.

@Aytaç 

This is apparently a bug in MacOS, and if you're still seeing it on an all-current system, they haven't fixed it.

If you look further up in the thread, I posted a procedure (with screenshots) to determine what the correct display of the file should be. It's pretty simple and straightforward. That will give you a baseline and it shouldn't be necessary to try all kinds of comparisons.

We have already determined two variables that affect this. One is LUT (table-) based monitor profiles. MacOS does not treat these correctly, and that seems to be pretty consistent. You need to use matrix-based monitor profiles on a Mac.

The other is the color management engine. It seems that the Apple color engine shows less symptoms than the Adobe color engine. That in itself qualifies as a bug, of course, it should display correctly in both cases. This isn't open to interpretations.

Run the procedure I described directly above your post. This will determine what the correct appearance on screen should be. The immediate impulse is to assume the high-contrast version is correct, but in fact it's usually the opposite. Higher contrast often indicates excessive/incorrect clipping.

We've seen quite a few of these in the forum, all on Mac. Apparently it's a bug in MacOS's GPU driver component.

One thing we've established is that LUT (table-) based monitor profiles don't work well in MacOS, and excessive black clipping is the common symptom. If you're using LUT profiles, rerun your calibrator, this time set to make a matrix monitor profile.

Other users have reported that switching from the Adobe color engine to the Apple color engine improves it. It's still a bug, it should work with both color engines, but sometimes the main thing is just to get back in business.

What I see in these screenshots is channel clipping.

In example #1, ACR clips the red channel. The other two channels are unaffected.

In the jpeg, #3 shows blue channel clipping. The other two channels are unaffected.

This kind of channel clipping is historically typical of a bad/defective monitor profile - but here's the thing: the conversion into the monitor profile is executed in the GPU nowadays. That means a buggy GPU driver can throw the conversion off, and that's what I think happens here.

In other words, monitor profile <> GPU driver is very much two sides to the same coin now. A marginal profile can throw the GPU off, and a buggy driver can cause the profile to fail. Both need to be in good order.

The lighter shadows is the correct version.

I've doubled checked here and I'm not seeing this on Windows. ACR and Photoshop are absolutely identical in the dark values. So there's nothing inherent in Photoshop.

ACR won't work without the GPU now, but LrC does, so you could try to disable the GPU there and compare again.