Android Studio 3 creates an adaptive icon for your app which is only available in SDK 26 and up. Launcher icons should be put into the mipmap folders.
If you look at your manifest, you can see that it references ic_launcher
android:icon="@mipmap/ic_launcher"
If you look in your mipmap folder, you see your normal 5 different launcher icons which will be used for anything lower than SDK 26. For SDK 26 and up, it uses the XML files from the anydpi-v26
folder to make use of adaptive icon.
<?xml version="1.0" encoding="utf-8"?>
<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
<background android:drawable="@drawable/ic_launcher_background"/>
<foreground android:drawable="@mipmap/ic_launcher_foreground"/>
</adaptive-icon>
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