When you drag a screenshot into the canvas, the display resolution is not taken into account.
For example, if a screenshot from an iPhone 17 Pro (1206 × 2622) is dragged and dropped into the canvas, it is inserted at a size of 603 × 1311 (i.e., half the actual size).
However, iPhone screenshots have a resolution of 144 × 144, or @3x. Accordingly, the screenshot size should be 402 × 874 (i.e., ⅓ of the actual size) when imported into the canvas.
