DIAGNOSIS This is a known USB-C handshake issue with the integrated hub. The monitor is briefly losing the video signal.
FIX First, disable the monitor's power saving features. Press the joystick button. Go to Menu > Display > Power > USB-C Power Savings. Set it to Off. If that doesn't work, update the monitor firmware using Dell Display Manager on your connected PC.
IF THAT DIDN'T WORK The USB-C cable is likely the culprit. Use the cable that came with the monitor. If you lost it, buy a certified USB-C 3.2 Gen 2 cable that supports DisplayPort Alt Mode and 90W power delivery.
HEADS UP Do not use cheap USB-C cables from unknown brands. They cause unstable power and signal delivery, which can damage the monitor's USB controller over time.