S2721D, black vertical line appeared

If the monitor is under warranty, call and they'll replace it.  If it's out of warranty, you can either live with the issue or replace the monitor -- even if you can find a replacement panel (they're generally not available), repair will cost more than a new 27" monitor will.

Update, This morning the Black line blinking and gone for 4-5minute, 
and return again. 
What would cause this ??

It's a faulty connection inside the LCD assembly -- the monitor needs to be replaced, or it will once enough lines have formed to make the display appearance unacceptable to you.

🥹🙇 Thanks Ejn63 , I'm try not to think about it.