Thanks for the reply. I still don't quite understand the relationship between "DSC supporting" and "one tb3 cable with two HBR3":
You have to think about what is supported by the GPU and what is supported by the display.
Intel GPUs support DisplayPort 1.2 (Ice Lake supports DisplayPort 1.4 and DSC but no Apple Mac uses that yet).
AMD GPUs before Navi support DisplayPort 1.4 without DSC (and Nvidia GPUs before RTX).
AMD GPUs starting with Navi support DisplayPort 1.4 with DSC (and Nvidia GPUs starting with RTX).
If you're including Thunderbolt, then some Thunderbolt controllers (Alpine Ridge, Falcon Ridge) support only DisplayPort 1.2 and some support DisplayPort 1.4 (Titan Ridge).
If you have a DisplayPort 1.4 GPU connected to an Alpine Ridge Thunderbolt controller (such as early Thunderbolt 3 Macs), then you can only get DisplayPort 1.2 out of the Thunderbolt controller.
1. If you want 5K resol., then you only need two HBR2, or two DP 1.2, no DSC, no problem;
Right. DP 1.2 supports HBR2. You can have a display with a Thunderbolt 3 connection that uses two HBR2 connections over Thunderbolt 3 to get 5K 10 bpc. Some PCs only have one connection to the Thunderbolt 3 controller. In that case, you would want a display that support 5K 8bpc with a single DisplayPort 1.4 (HBR3) connection such as the Ilyama 5K display, or you want a display that supports DSC (The only display I know that supports DSC is the XDR). An Nvidia GPU in Windows can deliver 5K 6 bpc using HBR2. I don't think macOS supports 6 bpc. I believe the LG UltraFine 5K and the Dell 5K do not support 5K from a single DisplayPort connection even at lower bit depths or refresh rates.
2. If you want 8K resol., then you need two HBR3, or two DP 1.4, and it has to be two physical DisplayPort cables, no matter if you have DSC;
That is true for the Dell UP3218K for 8K60. It also supports single cable 8K30. 8K60 can also be done using single HBR3 YCbCr 4:2:0 but I don't know if the Dell supports that mode. There may exist 8K TVs that support DSC.
3. If you want 6K resol., then you still need two HBR3, or two DP 1.4, but the dataset is small enough to fit into the single TB3 cable, no matter if you have DSC;
You don't need two HBR3 if the GPU supports DSC. If the GPU supports DSC, then it only needs HBR2 to get 6K60 (but the GPU still needs to support DSC which is part of DisplayPort 1.4).
4. In the case of 6K, whether supporting the DSC functionality or not only determines if the rest bandwith of the Thunderbolt3 cable supports the high speed USB transmittion.
Yes, with DSC, you only need HBR2 to get 6K60 leaving plenty of bandwidth on the Thunderbolt cable for USB 3.0. The connection has to be Thunderbolt 3 40 Gbps to get that. If the connection were only USB-C (DisplayPort alt mode instead of Thunderbolt alt mode), then the 4 lanes would be used by the HBR2 connection leaving only the USB 2.0 line for USB data.[/QUOTE][/QUOTE]