Hi VonTippa21,
We understand wanting to only download apps from the App Store.
We did a search for Amazon Music using the Apple Services Marketing Tools. Currently it's only showing that Amazon Music is available as an App for iPhone, iPad, Apple Watch, and Apple TV. It does not show any apps that were removed from the App Store but we're not finding any reference on Amazon that it was available in the past.
We recommend that you reach out to Amazon to inquire if they have any insight on this. This resource can help:
How to contact an app developer - Apple Support
Contact the developer of an iOS, iPadOS, or watchOS app
1. Open the App Store on your iPhone or iPad.
2. Search for the app, then tap it. If you can't find it, tap the account button
or your photo at the top of the screen, tap Purchased, tap "Not on this [device]," then tap the app.
3. The app's product page appears. Scroll to the Ratings & Reviews section, then tap App Support. If you don't see App Support, make sure that you're signed in with the correct Apple ID.

We've added steps to find that information on the mobile version of the app since it's not appearing in the App Store for Mac.
Hope that helps!