Yes vatsav, I found a fix  I bought a 4k 60hz hdmi - type-c cable and it's working like a charm. On the macbook it works at max rezolution [NAME].   The flickering at 60hz / 30hz will persist for ~1h after connecting a device with hdmi-type-c cable that is only capable of 2k resolution, or 4k 30hz. You should connect back display port and use it at 144hz and the flickering will disappear in 1h. 
Hi Chris, I have just bought a DELL AW3821DW. I use it on windows with rtx 3080 and on Macbook Pro 15 late 2018. For both of them with Display port. I have a flickering issue with it at 60hz on Mac. The monitor OSD menu is also flickering (unstable image), when you try to change the input source. On 144hz neither the window nor the OSD are flickering. This started to happen after I initially connected the macbook through a docking station made by Atzebe with HDMI to the monitor. Another big issue is that if there is no input source on the default one, it does not automatically switch to the input source that has signal. This is really a bad thing because I have to go to the monitor menu at least two three times a day, when I disconnect and reconnect my macbook. Is there any firmware upgrade I can do to fix these issues ? Or at least a way to make the monitor work again fine on 60hz ? Now the issue is on both Mac and Windows at 60hz. If my last device used with it used it at 60hz, the OSD will also flicker. If last device used it at 144hz, then the OSD is not flickering.  Best regards, Alin
AW3821DW, flickering at 60Hz, works fine at 144Hz