Onboard  Iris Xe Graphics certainly is capable of Driving that resolution at 60hz,  2 possible point of failures are Bad HDMI port ( motherboard) or Bad driver.    First download a copy of Drivers from Support Site and Pause windows updates.   [URL]   Reboot to Safe mode and use DDU (display driver uninstaller) to remove the current driver.  Reboot again and install the driver posted above and test it .  If it works fine than resume windows updates and check if windows update is trying to download an intel driver or not.     
Hi all, I have a Dell Latitude 7420 I would like to connect an ultrawide screen monitor "Monoprice 43in CrystalPro Curved Monitor - 1800R, DFHD, 120Hz, DisplayHDR 400, AMD FreeSync, Quantum Dot " via HDMI directly.  Actually, I used the same monitor without any problems on my previous Dell Latitude 7410. However, when I connect the new Latitude 7420 to my external monitor, the computer basically breaks down. It sometimes results in a frozen setup, sometimes returns a blue screen, etc. I also tried to shout down the internal monitor but it did not help. I usually use the recommended resolution of 1920x1080 60Hz on my internal monitor without any problems. At the moment, I try to use only the external monitor (internal monitor is switched off in the settings) and my Windows operating system automatically selects the recommended resolution of 3840x1200 at 60 Hz for the external widescreen monitor. Thank you very much in advance for your help!    
Dell Latitude 7420 with external ultrawide monitor