Thunderbolt dock vs Thunderbolt display?

[GFLPraxis]

Hello all! I have a 16" MacBook Pro w/M1 Pro, so, max 2 displays.

Right now, I am running 1 display off of it (1440p ultrawide via USB-C to DisplayPort cord), planning to go to two.

I was intending to get a ThunderBolt dock to run everything. But I've been offered a used LG UltraFine 5K Thunderbolt display (the one designed for Macs).

Is there any point of getting a Thunderbolt dock in that case? I was thinking I could just daisy chain the 1440p display off of the 5K display, then add the USB-C to Ethernet adapter and USB-C to USB-A hub I already have to the Thunderbolt display, and have 100% of the same functionality. Am I missing anything?

 

[Amethyst1]

I was thinking I could just daisy chain the 1440p display off of the 5K display, […]

You cannot do that, since the LG UltraFine 5K doesn’t have a second (downstream) Thunderbolt port.

The reason is that a Thunderbolt 3/4 port carries two DisplayPort signals, both of which are used by the LG UltraFine 5K in a “dual-link SST” setup, i.e. each of the two signals drives one half of the monitor.

 

[GFLPraxis]

You cannot do that, since the LG UltraFine 5K doesn’t have a second (downstream) Thunderbolt port.

The reason is that a Thunderbolt 3/4 port carries two DisplayPort signals, both of which are used by the LG UltraFine 5K in a “dual-link SST” setup, i.e. each of the two signals drives one half of the monitor.

But the second monitor wouldn't be a Thunderbolt display, it would be USB-C (and only 1440p). Would that change anything?

 

[Amethyst1]

But the second monitor wouldn't be a Thunderbolt display, it would be USB-C (and only 1440p). Would that change anything?

No. You cannot daisy-chain another DisplayPort/Thunderbolt/USB-C monitor to the LG UltraFine 5K.

A workaround would be to use a DisplayLink adapter to hook up the other monitor to the UltraFine’s downstream USB-C ports. But that isn’t as good as hooking up the monitor directly to the MBP since the CPU is doing all the work that is normally handled by the GPU.

 

[joevt]

But the second monitor wouldn't be a Thunderbolt display, it would be USB-C (and only 1440p). Would that change anything?

None of the downstream USB-C ports of the LG UltraFine 5K has a DisplayPort capability. Same for Apple Studio Display and Apple Pro Display XDR.
The LG UltraFine 4K has a downstream Thunderbolt port that can be used for a display.

Since a Thunderbolt port can carry only two DisplayPort connections, and the LG UltraFine 5K uses both of them to achieve 5K60, a Thunderbolt 4 dock or hub cannot be used to provide DisplayPort connections for the LG UltraFine 5K and another display (that would require 3 DisplayPort connections, or the LG UltraFine 5K would be limited to 4K60).

The Apple Studio Display and Apple Pro Display XDR can use Display Stream Compression (DSC) with a single DisplayPort connection from Thunderbolt, which allows using a Thunderbolt 4 dock or hub to connect one of each or two of one or one of those and another display.

Windows and Linux can use MST to connect multiple displays with a single DisplayPort connection.

 

[Amethyst1]

The LG UltraFine 4K has a downstream Thunderbolt port that can be used for a display.

It’s worth mentioning that this only applies to the newer 23.7” model, not to the older 21.5”.