I've asked this question here a few times on how to adapt HDMI to USB-C (not the commonly available adapters for doing this another way around).
Now, I've found the solution.
C-Force has an IO hub that's designed for their USB-C monitors. CF120 is the part number. t's supposed to adapt HDMI to USB-C using alt mode and also handle USBPD splitting.
If anyone needs it, give it a try.