Recently I tested something that works.
I bought a Wimaxit1560CTV2 touch screen which has HDMI input but also USB-C.
It worked over HDMI or USB-C (except for touch) via UHD 630 and my 32" Philips 325E curved main screen works with my Radeon RX570.
I wanted to connect the 15.6" Wimaxit screen via USB-C to have fewer cables and lower consumption.
Only my Asus thunderbolt EX 3 card (alpine ridge NVM 26) has only one thunderbolt port and I needed 2, 1 for the USB-C screen and 1 for my Antelope DS8SC.
So I found a used Asus thunderboltEX 3 TR card (titan ridge NVM 56) with 2 thunderbolt USB-C ports.
The problem is that my Asus prime Z390-A motherboard is not given by Asustek as compatible with this thunderbolt card!!.
So I replaced my old TBEX 3 card with the TBEX3 TR model but without being able to connect the internal TBC cable because it has 14+1 pin TBC and my motherboard only 5 pin TBC!!.
I also didn't connect the internal 6 pin connector for the charging power supply.
I only connect the internal USB2 cable.
I just modified the bios to indicate 2 thunderbolt ports.
The card like the old one was located on PCI port 3.
Under W10 everything worked but under Catalina the thunderbolt Asus TR card is recognized under Hackintool as JHL 7540 but only the USB-C screen and my main screen worked.
Impossible to recognize my Antelope card whatever the different configurations I tried !!.
And then as a last hope, I changed my PCI port thunderbolt card and put it in PCI 2.
Modified the bios somewhat, deleted my "thunderbolt hackindrom ssdt" in acpi/patched and there everything worked, the USB-C screen ert my Antelope card.
Only the touch function of the USB-C screen does not work!.
Or rather it works but badly, like a second mouse with only one cursor for both!. The touchscreen is badly activated but I don't see how to do it..?
Maybe by flashing a modified firmware ??
To sum up, the Asus thunderboltEX 3 TR card works with the Asus prime Z390-A motherboard but without connecting the internal TBC and placing it on PCI port 2.
If interested I will post my EFI and my ioreg and the photographs of the bios modifications..