So if I understand this correctly,
Apple sells a MacBook Pro that has USB-C ports that support the Thunderbolt protocol (3 or 4, depending on MBP) and USB protocol (3 or 4).
Both of these protocols can incorporate the DisplayPort protocol.
These USB-C ports work correctly and support all of the standards that Apple claims that they do, including DisplayPort MST, HOWEVER, macOS does NOT support DisplayPort MST (at least not over the USB protocol).
This means that running Windows on the MacBook Pro computer does takes full advantage of the DisplayPort MST via USB protocol and the problem is not with the MacBook Pro or the USB-C ports, but rather with macOS and the software support for DisplayPort MST via USB protocol?
Is this Correct?
Can anyone verify that a dock using Thunderbolt protocol can support DisplayPort MST?
I believe the problem lies with many companies selling docks and stating that they a "USB-C" dock, but not clarifying which protocol they are using.
Ex. Anker 575 USB-C Docking Station (13-in-1)
https://us.anker.com/collections/hubs-and-docks/products/a8392?variant=37438617944214
They state that "macOS only supports Single-Stream Transport (SST) and doesn't support Multi-Stream Transport (MST)"
This dock appears to use the USB protocol, however it is not clearly stated.
CalDigit TS3 Plus Dock
CalDigit TS3 Plus Dock - Apple
They state that "Whether you need to connect dual 4K 60Hz monitors* or a single Thunderbolt 3 5K 60Hz monitor, the TS3 Plus offers next-level visual fidelity.
External dual display support requires a Mac with an Intel processor and Thunderbolt 3 ports.
*The TS3 Plus supports dual 4K displays from either the DisplayPort port (which requires an active adapter if converting to other video interfaces such as HDMI) or the Thunderbolt 3 port (compatible with USB-C video adapters such as HDMI, VGA, or DisplayPort)"
This is a Thunderbolt dock, however it only has one DisplayPort connection and the other display needs to use the USB-C port to connect the display.