I would say the vertical line is the standard gap between columns which is 20px by default in Elementor. You can set it to zero, but another solution might be is adjusting the background color of the page. My guess is, looking a the left picture, you set the background color in the columns to black, but the page background color is white.
But what confuses me is that the line goes through the picture in the example on the right. If this is one picture, normally it would be in one column. So there would be no column gap.
One way to do it, is when you are on the page inside the Elementor editor: - Go to the section where the problem occurs, click on the blue handle. - In the editing menu go to the first tab (Layout) - The second setting is 'space between columns' (or something like that, mine is in Dutch). - Set it to 'none'.
At least this works for me, but I don't use a theme.