You’ll need to create three sets of screenshots, each containing 4–9 screenshots. These can be shots of the same screens, but taken on different devices.
You can find information about the corresponding devices for each set at the following link:
https://developer.apple.com/help/app-store-connect/reference/screenshot-specifications
For Google Play, you need to prepare 4–8 screenshots in PNG or JPEG format, up to 8 MB.
Aspect ratio: 9:16.
Size: minimum 320 pixels, maximum 3,840 pixels.