Well, it turned out we were wrong. Also ACPU didn't output colors correctly (especially some full saturation primary (or close to) colors were somewhat dull.
The only software that saved me is ColorSync Utility. On the first print dialog you have to set the "Print as color target" option. Doing...
Yes, thank to help from another respected forum I've been told that ACPU works just fine under Catalina despite the misleading notice from Adobe. Printed the same Argyll targets and overall saturation seems to be greatly improved.
Taken from Adobe here [https://helpx.adobe.com/photoshop/kb/no-color-management-option-missing.html]:
"The Adobe Color Printer Utility is not supported on macOS Catalina 10.15 or later."
That's probably the main reason I opened this thread.
Beside that, is the Colorimetric Intent even taken...
Having reprinted the targets in Photoshop, with everything else as before, I now get much more plausible results.
It seems I've lost a lot on the darker tones: I'll have to make a few real world test prints.
Wireframe: OEM Ilford Smooth Gloss
Solid: Argyll custom profile
after trashing many A4 sheets of printing targets I just ralised that printing them in Qimage One (my preferred printing software) with "Color management OFF" mode, doesn't actually output the colors correctly. Red are super low satured and all other color containing reds...