Hi @vizualcenter , welcome to Thunkable! 
Be sure to check out our posts about How to ask Great Questions v2.0 and our Community Guidelines as you get started.
APK files from Thunkable cannot be installed for publishing to the Play Store. To do this, you would need to be on our Pro plan or higher and download the Android App Bundle (aab) which you could use to list your app on the Play Store.