P2720DC, use MST function on MacBook Pro 16

I contacted the Apple Hotline half an hour ago. I got information that this macbook pro supports this function, as well as the latest version of MacOS 10.15.5. The problem is also with the monitor. Please "don't bounce the ball" and help me.

@OmertaPL  As far as I know, macOS still does not support DisplayPort MST.  There have been complaints about this for several years on the Apple forums, these forums, and elsewhere on the Internet.  A cloned image is what happens when you connect a daisy chain setup to a system that doesn't support MST, so it sounds like Macs still don't support MST.

In that case, the only way to run multiple displays from a single connection on a Mac is to use a solution that taps into Thunderbolt 3.  The reason that works is that TB3 allows the system to send two independent GPU outputs over the TB3 link, so the Mac assigns one output to each display.  But even there you can only run TWO displays over TB3, whereas on a PC you'd be able to run 3-4 depending on the PC and the displays involved.  But DisplayPort MST requires the system to be able to split a SINGLE interface to drive multiple displays, and it seems Macs still don't allow that.

@OmertaPL  I'm not trying to "bounce the ball".  You can see for yourself the years of complaints about lack of MST support on Macs.  If that has changed recently, then I was unaware of that -- but do you have any official documentation about Apple adding MST support rather than just something you heard from an Apple Support rep?  Dell Support reps have been wrong about technical details plenty of times, so I wouldn't consider that an authoritative confirmation.

The only thing you need to do in order to set up a daisy chain is use either a DisplayPort or USB-C input on the first display in the chain, connect the MST output of the first display to a DisplayPort input on the second, and then enable MST mode on the first display -- although that last step is automatic on newer Dell displays once you connect something to the MST output port.  I know this because I set up display daisy chains on a regular basis.  And it sounds like you've already done that.  In that case, check your display settings in macOS.  Does your system recognize multiple displays?  If so, set them to Extend rather than Mirror.  But if the system only recognizes a single display, then it's not working with MST properly, and as I said, a cloned image is what you get when you connect a daisy chain to a system that doesn't support MST.  I'm sorry if you consider that "bouncing the ball", but there's nothing else for you to do on the display or cabling side at that point.  And if you want to test your daisy chain, connect to a PC that supports daisy chaining and see what happens.

@OmertaPL  Here is a thread from only one month ago talking about the fact that macOS still doesn't support DisplayPort MST.  And the person there actually notes that when they use Boot Camp on their Mac in order to run Windows on it, then the daisy chain works.

I understand, I read this thread. Unfortunately, I do not know why on the hotline they wanted to convince me that this function must work with this macbook and the latest version of the system.

Ok, I was based on what they told me on the Apple Hotline. The consultant checked their technical documentation and confirmed that the latest Macbook Pro and the latest iMac Pro have this function. It's like you say, it detects both monitors as one, there is no option to set them differently.

@OmertaPL  My guess is that they are confusing DisplayPort daisy chaining with Thunderbolt daisy chaining.  Thunderbolt daisy chaining DOES work, but it's only possible with displays that support actual Thunderbolt rather than just regular DisplayPort/USB-C.  But if you want to pursue this with Apple, then consider setting up Boot Camp on your system and installing Windows 10, even if you only do so temporarily.  Then you can follow up with Apple Support and say, "This daisy chain works as expected when I run Boot Camp on this system. But when I boot this same exact system into macOS, it doesn't work as expected."  My guess is that you will eventually get a reply back from the Apple Support rep basically saying, "I looked into this more and upon further research, DisplayPort daisy chaining is actually not possible on macOS. I apologize for the confusion."

They'll probably answer me that way. Unfortunately, for my current job, a more efficient solution is working on MacOS.

@OmertaPL  Then you can connect the displays to your system separately or get a Thunderbolt 3 to Dual DisplayPort adapter like this one, although in the latter case you'll be using your TB3 port purely for video output, meaning you would not get power or USB data from your displays the way you can right now when connecting over USB-C.

However, be aware that the P2720DC only provides 65W of power over its USB-C connection.  The MacBook Pro 16" is designed for a 96W source, so if you only have it connected to the display rather than keeping the MacBook's own adapter connected, then you might see slower battery charging and reduced performance because you're only giving your laptop 67% of the power it's designed to have available.  Some of Dell's higher-end U Series displays offer 90-95W of power over USB-C, but the P Series seems limited to 65W for now.

Yes, I know that. At this time, I just use two USB C outputs, of which one is connected to the charging port and this calmly enough for daily work under the current load.

Thanks for this discussion. I have a MacBook 12" - the one with just a single USB-C (non-Thunderbolt) port - and have just purchased the same monitor Dell P2720DC to reduce my cable burden. I was considering buying a second identical monitor as the reviews rave about the daisy-chaining abilities. 

First I did a simple GPU calculation - the MB12 can drive an external UHD display which has a resolution of 2.25 times the QHD of the P2720DC - so, given past experience of undocumented ultra-wide resolutions, I thought it would be OK.

Then I did a wider search to check for any issues and found a huge number of discussions documenting MacOS's inability to do DisplayPort MST. This discussion was the most recent and relevant, and the most convincing and utterly disappointing! 

As ever, Apple embrace the very latest technologies with every new product before ever milking the full potential of their previous ones, leaving owners abandoned well before their time. "USB-C with native DisplayPort 1.2" is forgotten in favour of the latest flavour of Thunderbolt. 

Clearly a third party has not developed a workaround.

Needless to say without a specific announcement from Apple, I won't be buying a second P2720DC!

T.