The App Store you connect to determines what apps you can see and download. Here's a more detailed explanation:

App Store Availability based on your Apple ID: The App Store you access is linked to the country or region setting in your Apple ID. This means Apple curates different app selections for various regions based on factors like legalities, content restrictions, and even local preferences. So, an app you see in the US App Store might not be available in the Australian App Store, and vice versa.

Not dependent on your Apple device: No matter which iPhone, iPad, or iPod touch you own, as long as you're signed in with the same Apple ID, you'll see the same App Store selection for your chosen country. It's the Apple ID that dictates the App Store, not the specific device you're using.