10 screens × 2 orientations = 20 standalone HTML files. Open each in Chrome, set the viewport to the exact pixel dimensions, and capture a full-page screenshot.
Open the file in Chrome → DevTools (F12) → Toggle device toolbar (Ctrl+Shift+M) → Click "Responsive" dropdown → Add custom device → Set width & height to the file's dimensions → Take screenshot (Ctrl+Shift+P → "Capture full size screenshot").
App Store allows up to 3 app preview videos (15–30 seconds each). These must be screen recordings of your actual app — open the app on an iPad Pro 12.9" (or simulator), start screen recording, navigate through key features, then trim to 15–30 seconds. The HTML files above are for static screenshots only.