After updating to both Tahoe 26.6.2 and Photoshop 27.9.0, image import color, with Adobe Color Engine selected in Color Settings, is broken

This is using a fairly new Mac M5 Max laptop with Lightroom Classic and Photoshop installed. Everything was “normal” as of a month ago (I normally work on images in Classic, then Edit in Photoshop to print, and I’d done some prints on this system, with the latest Tahoe and Adobe software, at that point).

This week, I went to make more prints, and now: Edit in Photoshop, from Classic, is “broken”: the image in Photoshop is lighter and desaturated. No way around this from the Lightroom side: any attempt at changing settings; or bypassing the direct Edit In step by saving to a JPG or TIFF; produces the same results. (I’m a color management expert, this isn’t “user error” by a novice).

Next step was to try on a different system. I have a Mac M4 Max laptop that’s running the latest version of Sequoia - not updated to Tahoe - with the same current version of Photoshop and Lightroom Classic installed. Moved my external drive (images and catalog) to that system, tried it: everything works fine, the color is correct. Implication is, the problem is the latest Tahoe release. (I have Golden Gate developer beta on yet another Mac laptop but haven’t tried it there yet). But anyway:

I went back to the M5 Max, played with Color Settings some more, then decided to try something obvious. I switched the rendering engine from Adobe Color Engine (ACE) to the Apple CMM. And doing that fixes it. Now the color is fine.

So the problem ends up being: Adobe Color Engine is broken and/or unavailable on the M5 Max with Tahoe 26.2. Doesn’t -seem- to be inherent in the Photoshop 27.9.0 build itself since “that build works on the M4 Max Sequoia system”. So my question (also as a developer) is: is ACE supposed to be built into MacOS, independently of Adobe software, and did it go “missing” in the latest Tahoe release? That would be one explanation. Or, is it installed as part of the Photoshop installation, and is it somehow “not installed” on my M5 Max with Tahoe 26.2, but yet it’s “still installed” on the M4 Max with Sequoia, where it’s functional?

I can work around this simply by switching to the Apple CMM for now. I’d prefer to get back to Adobe ACE for this workflow “just because”, even though I don’t expect the color processing pipeline to produce visibly different results that way.

Someone should look into this; I’m surprised that I’m not seeing any other reports. (Unless this is potentially a problem with my Photoshop install; in which case, should I remove it and reinstall it?)