Actually it turned out to be the opposite actually, there’s a DP to HDMI converter chip in-line between the USB-C port and the HDMI mux inside the PPM, this was confirmed here: Connecting laptop using USB-C cable - #21 by Philips_Support_P
There was a major confusion until engineering confirmed this to Prashant (and I can also confirm the Parade PS176 chip: USB-C Video Port not working with MacBook or other laptops - #59 by wernerj)
I wasn’t initially able to get the PPM recognized as a Alt-mode DP device, but this turned out to be because the USB-C firmware handling the USB-C video port was too old (this depended on when the PPM board was run through the manufacturing line). It can be updated in the field with a Windows machine: USB-C Video Port not working with MacBook or other laptops - #79 by IvoGrijt