Would this work if I had it connected to my iMac Pro and plugged my LG 5K into it? (I like to use the extra screen with this and my MacBook Air and would save me fishing round the back.) I suspect not but I don’t get the technicalities of it all 😂)
Display support: Should work fine. The Thunderbolt signal containing the two Thunderbolt DisplayPort 1.2 streams from the iMac Pro is passed through the hub to the LG 5K which converts the Thunderbolt DisplayPort streams back into DisplayPort (one stream for the left half and another stream for the right half).
Only the Apple Pro Display XDR has a problem with intermediate Thunderbolt devices between the display and host when the host does not support DSC. Without DSC, two DisplayPort 1.4 streams are used but that doesn't work without a direct connection and some trick of the Apple drivers (the problem is dual HBR3 streams would exceed 40 Gbps limit of Thunderbolt but 6K60 doesn't require all the bandwidth of dual HBR3 and Thunderbolt doesn't transmit the stuffing symbols of DisplayPort used to fill the HBR3 streams so it can work with Apple's trick - I think Windows drivers don't have the same trick so in that case you need a GPU that supports DSC?).
For non-Thunderbolt displays, the hub has three Thunderbolt ports and you can use any two of them for displays. This is a limit of the Goshen Ridge Thunderbolt controller used in the hub. The limit was chosen because there are no Intel Thunderbolt hosts that transmit more than two DisplayPort Thunderbolt streams. I wonder if the eGPUs that connect DisplayPort outputs from their GPUs to the DisplayPort inputs of their Titan Ridge Thunderbolt controller (Blackmagic and Sonnet 5500 XT/5700) can add DisplayPort streams to the Thunderbolt signal (in addition to the streams coming from the host). To connect 3 or more displays, only one can be HBR2 (4K60). The others need to be HBR (1440p60) or RBR (1080p60). Of course, no-one would do that since they could just connect additional displays directly to the eGPUs (there are no Thunderbolt HBR or RBR displays).
USB ports and bandwidth: I wonder if they added any USB controllers to fill up the Thunderbolt bandwidth of 22 Gbps? I suppose for USB4 support and to lower cost, they just chained a couple 10 Gbps 4-port hubs together internally so the limit for all 7 ports is 10 Gbps.
Old Mac support: people have shown with the OWC hub that Thunderbolt 4 hubs work with Thunderbolt 2 Macs running Big Sur. You can connect more than one Thunderbolt device to the hub. I haven't seen anyone explain what happens in Catalina.
Old macOS and boot support: OWC says you can boot from their Thunderbolt 4 Hub - I don't think there would be any difference in capabilities between Thunderbolt 4 hubs/docks except for the extra chips included that provide for the extra ports (probably all USB hubs and adapters). If you can boot from a Thunderbolt device, then it implies EFI support for all 3 downstream Thunderbolt ports. Doesn't that mean EFI has more support than Catalina (since Big Sur is required for these Thunderbolt 4 hubs/docks)? If EFI can enumerate all the devices and start boot of Catalina, then the enumerated devices should remain when the OS boots unless the OS un-enumerates them. Maybe all the ports can work in Catalina if you don't hot plug the hub?
Chaining multiple hubs: OWC says their Thunderbolt 4 hub needs to be connected directly to the host. If it's connected anywhere else then there is some loss of function (but they don't say what). CalDigit says you can connect the CalDigit Thunderbolt hub to the CalDigit TS3+. Neither mentions anything about chaining hubs together. I don't think there's anything in the USB4 spec that says you can't chain hubs.
