Android Studio - Flutter / Dart plugin not installed

Problem: Errors of Flutter / Dart plugins not installed were shown even though they were already installed.
[!] Android Studio (version 4.2)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.

Cause: The Android Studio was upgraded and the symbolic link was not updated.

Solution: Update the symbolic link:

ln -s ~/Library/Application\ Support/Google/AndroidStudio4.2/plugins ~/Library/Application\ Support/AndroidStudio4.2