it's not windowmode, fullscreen mode. (I added the black background on the right randomly because I thought the writing background would be white because I was trying to upload the image on the community. It's not window mode.)
isn't werid... right?
How to get rid of that line disappears by clicking once in window mode and then clicking on the full screen again. Something's wrong.......=)
At first, I thought it was a problem with Hidpi, but I compared it by changing the window magnification to 100/125/150/200, but the problem was not solved. As the writer says, it is solved by turning on the window mode and clicking the full screen button again, and dragging each panel (docking) slightly changes the left and right widths. And then the line disappears. It's a strange problem.