I am building an app that would like to publish to the Google Play Store and AppStore. Hence my question, what problems await me when I use Cupertino date picker, for example. By problems, I don't mean user problems, but rather license, etc.
Yes, you can use the Cupertino date picker and other Cupertino components in apps that are published on the Google Play Store. The Cupertino date picker is a user interface component that is part of the Flutter framework, which is an open-source project released under the BSD license. This means that you are free to use the Cupertino date picker in your app without worrying about any licensing issues.