External monitor flickers when certain images are displayed

I recently purchased a Dell P2415Q 4K Monitor for my MacBook Pro 15" Touch Bar 2018. When I connect the monitor to my MacBook using a Type-C to DisplayPort cable, the monitor would flicker when certain images are displayed.

Here’s a video of what the flickering looks like.

The monitor is not damaged, as I tried the same images using my Fire TV Stick and Cube (HDMI). It’s also fine when I hooked up my friend’s MBP 13” Touch Bar 2017 (the same C-DP cable), there is no flickering whatsoever.

I tried switching cable, and no luck (and wasted 17 dollars). The only thing I can think of is the Radeon GPU—which Mac automatically uses for external display.

Did anyone else have the same issue before? I already scheduled a Genius Bar session. I just want to check if there is already an existing solution (no luck with all kinds of Google search either).