I tried following this tutorial: https://pub.dev/packages/flutter_launcher_icons

So I set these keys in my pubspec.yaml:

dev_dependencies:
  flutter_test:
    sdk: flutter

  flutter_launcher_icons: "^0.14.1"

  # The "flutter_lints" package below contains a set of recommended lints to
  # encourage good coding practices. The lint set provided by the package is
  # activated in the `analysis_options.yaml` file located at the root of your
  # package. See that file for information about deactivating specific lint
  # rules and activating additional ones.
  flutter_lints: ^4.0.0

flutter_launcher_icons:
  android: "launcher_icon"
  ios: true
  image_path: "assets/images/icon2.png"

and executed:

flutter clean
flutter pub get
flutter pub run flutter_launcher_icons

Get noticed some outdated packages, but I thought it should still work:

Resolving dependencies... 
Downloading packages... 
  collection 1.18.0 (1.19.0 available)
  leak_tracker 10.0.5 (10.0.7 available)
  leak_tracker_flutter_testing 3.0.5 (3.0.8 available)
  material_color_utilities 0.11.1 (0.12.0 available)
  meta 1.15.0 (1.16.0 available)
  string_scanner 1.2.0 (1.3.0 available)
  test_api 0.7.2 (0.7.3 available)
Got dependencies!
7 packages have newer versions incompatible with dependency constraints.
Try `flutter pub outdated` for more information.

flutter pub run flutter_launcher_icons succeeded without issues. I later tested that it actually found the file by letting it look for a file that doesn’t exist and it threw an error as expected:

Deprecated. Use `dart run` instead.
Building package executable... 
Built flutter_launcher_icons:flutter_launcher_icons.
  ════════════════════════════════════════════
     FLUTTER LAUNCHER ICONS (v0.14.1)                               
  ════════════════════════════════════════════
  
• Creating default icons Android
• Adding a new Android launcher icon
• Creating mipmap xml file Android

WARNING: Icons with alpha channel are not allowed in the Apple App Store.
Set "remove_alpha_ios: true" to remove it.

• Overwriting default iOS launcher icon with new icon
No platform provided

✓ Successfully generated launcher icons

After executing all this and running the app via usb debugging on my android mobile phone, the app no longer has an icon (what I called invisible above). Before that it showed the generic flutter icon.

I have repeated the process with flutter pub run flutter_launcher_icons:main and dart run flutter_launcher_icons instead and have also tried removing the alpha channel from the icon. This didn’t change the result. The icon is a 512×512 png.

I am unsure on how to debug this issue further.