Ok, I was able to solve this issue. You have to open the "intel graphics control panel" - click on screens - then make screen 3 copy 1&2Now all 3 screens will show the same aka duplikate.
Dell Laptop 5420 - Docking Station Model WD19TBS - Windows 10. Hi,I am unable to duplicate the screen from my Laptop to 2 Monitors.  Monitor 1 - LaptopMonitor 2  ( Display on Desk ) is connected via DisplayPort port to Docking Station,Monitor 3 ( Smart Display ) is connected via HDMI to Docking Station Display Settings when I select Monitor 1 (laptop) > Duplicate to  2 and 3  it only Duplicates to Monitor 2 and Extends to monitor 3. No matter what I try it will only duplicate 1 screen and extend the other.I had this working a couple of months ago when we were testing the Docking Station before purchasing a huge number of them. But now it wont work anymore. I updated all the drivers, checked the settings, cables, etc...Any help is appreciated.Thx
Duplikate Laptop 5420 - 2 screens using WD19TBS Dockingstation