There are several online tools available that can help you generate screenshots for different sizes required by the Apple Store. Some of the popular ones are:
- LaunchKit: https://launchkit.io/screenshots/
- AppLaunchpad: https://www.applaunchpad.com/
- Screenshot Builder: https://screenshotbuilder.com/
You can upload your existing 16:9 screenshots to these tools and they will generate screenshots for all the required sizes. However, it is recommended to have separate screenshots for portrait and landscape modes, as it provides a better user experience and helps showcase all the features of your app.
If your app doesn't support landscape mode, you can still upload portrait screenshots for the required sizes and leave the landscape ones blank.
Here's an example of how you can use LaunchKit to generate screenshots:
1. Go to https://launchkit.io/screenshots/
2. Click on "Create New Project" and enter your app details.
3. Upload your existing 16:9 screenshots.
4. Select the required device types and orientations.
5. Click on "Generate Screenshots" and wait for the tool to generate the screenshots.
6. Download the generated screenshots and upload them to the Apple Store.