Macbook Pro 2016 low resolution with External Monitor (Dell U4021QW)

Connecting to displays over 4096 pixels wide requires Big Sur AND (for MacBook Pro older than 2017 models) TWO interface cables. The picture is re-assembled into one with Picture-By-Picture feature of the display and the Arrangement pane in the Mac:

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I'm planning to buy exactly the same monitor but I've a Macbook Pro 15" 2017 (https://support.apple.com/kb/SP756), so slightly newer. However I think the hardware is more or less the same. I can't believe that the LG 5K (Apple) monitor does work with just one cable via Thunderbolt and the Dell does not. How can this be explained? It's really not a solution to split the screen into two!

Did you find a solution beside of "two cables"?

If the virtual displays are in the reverse order left-to-right, either swap their cable or drag the "Icon" of one screen to the other side.

If you have a Menubar on each display, disable this feature and the screens will merge into one "extended desktop"

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Input Connectors

1 x DP 1.4 ( HDCP 2.2) ( 10 bit Color @ 60HZ)

2 x HDMI 2.0 ( HDCP 2.2) (10 bit Color @ 30HZ)

1 x Thunderbolt(TM) 3 ; (Alternate Mode with Display Port 1.4, super speed USB 3.2 Gen 2 (10Gbps) Upstream , Power Delivery upto 90W*) , certified for Windows® and Mac® 

So probably one ThunderBolt, one DisplayPort would be most likely to be trouble-free.

Possibly two HDMI since each would then be "ordinary" resolution. (High resolution and HDMI is an oxymoron.)

Although this may personally make you crazy, your complaints of having to have the MenuBar on top of the left half-display and the Dock at the bottom of the left half-display are not that awfully different from the way it would work on one large display. You could lo use Dock-on- left, but that would take some additional getting used to.

The real question is, can you park a window half on each virtual display and have it scroll as one? If you can, the feature works as designed.

I just found out that the Alpine Ridge (Chip for TB3) only supports DisplayPort 1.2 -> which itself only support "3840 x 2160 @ 60 Hz". So far from technical point users with Macbook Pro 15 2016-2017 do really need two cables to get 5k60. Very strange that apple this doesn't mention on their support page.

@tmartin1986: how does the display feel with the split screen?

<< However I think the hardware is more or less the same. >>

Your statement as written is NOT correct.

The processor used in the 2016 models is a 6th generation SkyLake series processor, with integrated Iris 540 or 550 graphics. Apple does not support displays wider than 4096 pixels on this MacBook Pro, forcing you to use multiple display cables to support an extremely large display.

The processor used in the 2017 models is a 7th generation Kaby Lake processor, with Integrated Intel graphics 640 or 650 graphics processor. Apple does support display wider than 4096 pixels wide on this processor, but only on Big Sur and later.

Ok got your point, but you are going into the wrong direction - we are speaking about the 15" models. The 15" Macbook Pro are using a dedicated GPU, the intel graphics shouldn't be involved at all. But to be correct, yes, the dedicated GPU isn't the same for 2016 and 2017 models.

But both model-years share the same TB3 chip (Alpine Ridge) and in my understanding this little guy is the culprit as it supports only DP 1.2. Correct me please if I'm wrong.

EDIT: btw my Macbook Pro 15 2017 has a Intel HD Graphics 630 and NOT a 640 or 650! And I'm using the top model from this model year.

Between the picture-by-picture and the mac's ability to Arrange, it really does "put the two halves back together".

I found an explanation why Apples 5K display can use only one TB3 cable although it's only DP1.2:

https://www.reddit.com/r/hardware/comments/9sx2rj/mac_mini_and_macbook_air_support_5k_displays_at/