Found another user that was nice enough to post a screenshot. Problem is, that does not show what I expected.
I tested this myself a good while back with an AMD 6000 CPU and an older Win11 version without the USB4 panel.
And I recall reading over some threads here, where users reported situations, where their dock would not output a 2nd DP connection on FW13 AMD and took that as confirmation, that my experience must have been representative.
Has anybody with an AMD FW managed to extract 2 DP connections / tunnels through a single USB4 connection? Or is it more that Windows thinks there are 2 DP connections, but it never actually works?
To reliably show that AMD’s USB4 implementation can do that, we would need some kind of TB3 or TB4 dock, that internally uses both / can use both DP connections. Any TB4 hub (3 TB-outs) is the easiest, as if that drives more than 1 display, it is because there are 2 DP connections.
But docks with MST can still be used, if they give access to the 2nd connection, even if not intended.
For example, my Dell WD19TB dock uses only a single DP connection internally for the DP & HDMI outputs (using MST), which is why all of those also work on USB-C/DP Alt mode.
If any of those outputs are in use for 1 monitor, the TB-out on that dock can provide a 2nd DP connection if the host provides one (although it will be throttled, due to the dock prioritizing its main outputs, but it will still detect a monitor and allow to drive that at like FHD@60).
Just as a warning: The Lenovo TB4 dock is weird. While it’s TB-out it labeled TB and can do that, it is wired up in 2 different ways and can also be driven via MST on non-TB/USB4 hosts. So a 2nd display on that dock, even when using the TB-out would not be conclusive by itself and would require deeper investigation, which mode the dock internally chose to make that work.
Windows 11 also has a somewhat hidden debug option that can visualize the connections / tunnels through TB/USB4 in case someone is interested. This is behind the “Device Portal” under System>For Developers. Requires enabling Developer Mode, installing the Device Portal feature and rebooting after enabling it (can also be quickly disabled again just by flipping the Device Portal switch off). That hosts a website locally (by default only available from the device itself) that has a USB4 page that will sketch out the entire USB4/TB3 topology including active USB3, PCIe & DP tunnels.
(Here a screenshot of what that would show. near the root of the topology you can see the 2 DP tunnels and to which device/port they are routed to)
Edit: Oh and for my Linux friends: the “/sys/kernel/debug/dri/1/amdgpu_mst_topology” sysfile should report enough about the MST-topology to determine whether MST is involved or any given monitors are sharing a DP connection. Sadly I do not know better ways to debug how TB/USB4 uses DP tunnels.