Response from Dell via PM:

"As informed earlier, the monitor is not tested for the latest versions of macOS and can cause issues.You may have to look into options of upgrading the monitor to the one that is tested to work fine on macOS 10 and above to have this taken care of."

A monitor manufactured in September 2019 is apparently "not compatible with MacOS 10" and should be replaced.   This came after asking me to "try the monitor with a Windows laptop" and see "if the problem persists". 

Needless to say, I think this response is:

a) probably  

b) not very helpful.

I also note that the web page for this current model mentions nothing about MacOS whatsoever: https://www.dell.com/en-us/work/shop/accessories/apd/210-arcl

Dell, you really need to up your customer support game here!

I note that the August firmware update for this monitor mentioned some fixes to USBC power management.  After rebooting, the Mac laptops show a crash report with a stacktrace that is clearly in the dell display driver.  Either this is code Dell wrote, or code that Apple wrote.  Either way it seems like something that Dell should 

a) care about a lot, and

b) if they can't fix it, they should add a large compatibility warning to their product page or remove the item from sale.

Super unimpressed so far.

I'm having the same issue. It doesn't have to be be overnight, less than an hour seems long enough to crash the laptop. It is SUPER ANNOYING when I forget to unplug and come back to a crashed machine.

Dell needs to do more than say "use Windows" since they have firmware updates written for macOS. Clearly the monitor is supposed to support Mac laptops.

The Mac package is just an app that updates the firmware over USB.  It contains firmaware version M3B106 from August 2019.  My monitor was manufactured in September and is already running M3B106.

However ... when I look at the 'Windows 10' packages, I noter that there is a newer firmware version M3B107 from November,

https://www.dell.com/support/home/us/en/04/drivers/driversdetails?driverid=4mv3r&oscode=wt32a&productcode=dell-u3419w-monitor

The release notes say:

Fixed: USB-C video connectivity issues with Dell Latitude 3000 series

Maybe this will fix the problem we are seeing?

It should be possible to upgrade the monitor by borrowing a Windows10 laptop.  Or maybe Dell could update their Mac download page with the newer firmware?

I updated the firmware to M3B107 by borrowing a Windows 10 Laptop with a USBC display output.I left one of my MacBook Airs connected to the monitor and within an hour it had crashed and rebooted.

This is really not good.

Another response from Dell, which basically boils down to "don't buy a Dell monitor if you have a Macbook". I will be adding a review to the monitor's web page to warn others, because this is frankly pathetic.

From: DELL-Cares
Date: 02-03-2020 05:48 PM
Thank you for getting back to me with your observation. The monitor usually uses native drivers from the system that it is connected to and as the drivers are crashing, I request you to have a check if there are any updates for the MacBook that needs to be installed. Having said that, I would like to let you know that the monitor is not tested to work on a Mac OS 10 and the issue here could be with the compatibility as it is not showing the same behavior when used on a Windows machine. Our scope of support is limited in this case. I request you to get your MacBooks checked and make sure that the monitor specifications are compatible with the MacBooks.
Prajwal

At the top of this Monitors Forum board, read the Pinned posts = Dell monitor, Apple FAQ