Nothing stalls a submission like a screenshot rejected for the wrong dimensions. Apple accepts a specific set of sizes, and a frame that is even slightly off gets bounced. The good news is you only need to get this right once.
The sizes Apple actually asks for
You do not need a set for every device. Apple lets one large iPhone set and one large iPad set cover the whole lineup, scaling down to smaller screens automatically. Design for the largest in each family and you are covered.
Why exporting from a design tool goes wrong
General design tools do not know about App Store requirements. It is easy to nudge a frame, crop a hair short, or export at the wrong scale. Each of those is a rejection waiting to happen. A tool built for the store designs at the exact required resolutions from the start.
A frame is more than a rectangle
Real device bezels, corner radii, and safe areas make a screenshot read as a genuine product shot rather than a flat mockup. Using accurate frames also keeps your content clear of the notch and rounded corners, so nothing important gets clipped.
Design at the exact sizes App Store Connect expects, with real device frames. No guessing, no rejections.