It’s android studio default functionality, to remove the background edit ic_launcher.xml (anydpi-v26) and ic_launcher_round.xml (anydpi-v26) and set the background as “@color/transparent”.

https://help.infixsoft.com/wp-content/uploads/2019/12/image-1-1024x711.png

ic_launcher.xml (anydpi-v26):

<?xml version="1.0" encoding="utf-8"?>
<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
    <background android:drawable="@color/transparent"/>
    <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
</adaptive-icon>
ic_launcher_round.xml (anydpi-v26)

<?xml version="1.0" encoding="utf-8"?>
<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
    <background android:drawable="@color/transparent"/>
    <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
</adaptive-icon>