Google Pixel 7 Pro screen size and resolution
The Google Pixel 7 Pro has a 6.7-inch display at 1440 × 3120 pixels, an aspect ratio of about 19.5:9. A full-resolution screenshot from it comes out at exactly that size, and that's the image you drop on the mockup's screen.
Using it on Google Play
A raw Google Pixel 7 Pro screenshot is 2.17 times as tall as it is wide, over Google Play's 2:1 limit, so the store won't take it as it is. Put it inside a 1080 × 1920 frame with the phone around it and it fits the 9:16 size Google recommends.
