Further update. The Dell Customer support acknowledged the issue and they are replacing the faulty monitor. 
Today, my U4919DW started to flicker quite severely. When the flickers starts it shows severe moire and some ghost icons popping up. This is the second time this happened, but unfortunately everything I tried before to fix it, doesn't work anymore: factory resetting, completely unplugging it from power for like 30 minutes. changing temporarily the refresh rate to 30Hz.  This happens on my Windows PC, Macbook M1, and MacBook Pro 2017. Here is a photo of the ghosting. I also have a 4K/60FPS video of the issue. But uploading on YouTube to share the link it gets compressed and the flicker removed. [IMAGE]   Any help of suggestion appreciated. This is still under warranty. 
U4919DW, entire monitor flickering