Diagnosis
This is a known USB-C handshake issue with the integrated hub. The monitor is briefly losing the video signal.
How to Fix It
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.