Here's how you can check download number for Android app -
Go to https://play.google.com/apps/publish/ & login with your google developer credentials.
On the first page, you'll see the active download numbers.
Here's how you can check download number for iOS app -
Go to https://appstoreconnect.apple.com/ & login with your apple developer credentials.
Go to App Analytics.
App downloads are measured as Units.
Hope this article was helpful :)