My app icon is not showing on some devices

Remove this line..

android:roundIcon="@mipmap/ic_launcher_round"

My issue was solved by restarting the phone.

Try This;

File -> New -> Image Asset -> Launcher Icons (Adaptive and Legacy)

For more information; https://proandroiddev.com/android-adaptive-icons-are-easier-than-you-think-3c66be2dd4dd

https://developer.android.com/guide/practices/ui_guidelines/icon_design_adaptive