Hi Mark
Thanks for responding to this and I understand the difficulties at this time. I'm very impressed with the colour management work you have done since I last saw AP a few years ago. What you have said in that the image should go darker or to the ST2084 transform is what I would have expected. But this doesn't happen. With Win10 HDR activated the Asus PA32 is definitely in PQ mode (you need this to get EDID working with HDR to get the ENABLE HDR active). EDID was double checked with HDFury Integral2. To see what was actually happening I created an image stack of test patches from Lightspace (https://www.lightillusion.com/) and measured these with my CR100 probe in a manual mode that Lightspace has. This showed that the response from the patches within the AP window had a 2.2gamma. I could get 1000nit, so it was "HDR" sort of and the Enable HDR was active, but not a ST2084 EOTF. I have tried various icc profiles such as a ST2084, Null (linear), and also unmanaged. The OCIO REC2020 ST2084 1000Nits was more linear and the luminance very low, quite strange. The other thing to consider is that monitors such as the PA32UCX have 2 calibration slots and other high end HDR monitors that may be used won't output EDID but you still want the HDR capability to be engaged, so having the capability to manually set this should be available. Please see two images, both showing the response of the patches in HDR one against (black line) 2.2gamma (1) and the other against an ST2084 P3 1Knit (2). Please note again the monitor was set to a St2084 EOTF (PQ) response and this was verified through measuring with Lightspace - ASUS_PA32_PQ. I'm not sure about the ROG-PG27 and its HDR mode but I will try and get some details from ASUS.
I have also attached two profiles created with Displaycal synthetic profile creater (Argyllcms) with one for pure 10K PQ 2020 and the other a PQ 1Knit_P3.
Stay safe.
PQ_1K_NIT_P3_D65.icm
PQ_10K_2020_D65.icc