To protect you, Google will prevent you from downloading older apps from its Play Store

Google has decided to tighten its policy of publishing applications in its Play Store to better protect its users. Therefore, the publisher does not want developers to use older Android APIs.
These functional libraries, in fact, evolve with each new version of the mobile operating system, improving not only the usability of the OS, but also security and privacy, with Google placing more emphasis on the last point. Pronunciation for about two years.

Using API monitoring is risky, and Google will clean up after introducing a new rule from November 1st. About applications that have been using APIs compatible with version of Android for more than two years.
From November 1, they will have the API level associated with Android 11 (Level 30) or Android 12 (Level 31). If they do not meet these criteria, they will no longer appear in the Play Store, with a few exceptions.

So, users who have already installed the standby app can continue to view it in the Play Store and reinstall it if needed. This also applies to owners of mobile devices that use an older version of Android.
In short, this rule is important for users who use the latest version of Google’s operating system. So they can no longer see old apps in the Play Store.

One year delay for new applications

This new rule completes what Google has already implemented since Android 9.0. For newer applications, the API status should not exceed one year for acceptance in the Play Store, taking into account August 1, as shown in the diagram below.

Currently, developers can still offer apps with API status associated with Android 11. But from August 1, they will be compatible with Android 12.

The editor sets the same time period of one year for updates, but gives developers a little more time. In fact, new applications will have to make the necessary changes from August 1st to November 1st.
Finally, Google provides Help Migrate and reach the API level required for visibility in the Play Store.

However, for Mountain View, developers need to use the latest APIs to ensure optimal security for Android users. It is true that you can ignore this by installing APKs outside the Play Store, but it will be done at your own risk.

Proof : Google