Material widgets implements the Material design language for iOS, Android, and web.
Cupertino widgets implements the current iOS design language based on Apple’s Human Interface Guidelines.
Why write a Cupertino app?
The Material design language was created for any platform, not just Android. When you write a Material app in Flutter, it has the Material look and feel on all devices, even iOS. If you want your app to look like a standard iOS-styled app, then you would use the Cupertino library.
You can technically run a Cupertino app on either Android or iOS, but (due to licensing issues) Cupertino won’t have the correct fonts on Android. For this reason, use an iOS-specific device when writing a Cupertino app.
You’ll implement a Cupertino style shopping app containing three tabs: one for the product list, one for a product search, and one for the shopping cart.
If you wish to read more on Cupertino and Material. Check the link below:
You can also use a flutter package called flutter_platform_widgets to check which platform your app is running on and use specific widgets(either Material or Cupertino)
This package link is : flutter_platform_widgets
I hope this helps