E: Package 'qt5-default' has no installation candidate

I apologize for the confusion. It seems that the 'qt5-default' package is not available in the default package repositories for your system.

To install Qt on your Raspberry Pi, you can follow these steps:

1. Update the package lists by running the following command:

   sudo apt update

2. Install the necessary dependencies by running the following command:

   sudo apt install build-essential libqt5gui5 libqt5core5a libqt5dbus5 qtbase5-dev

3. Verify if the Qt installation was successful by running the following command:

   qmake --version

If the command displays the version information, then Qt is successfully installed on your Raspberry Pi.

Please note that the package names and installation process may vary depending on the specific version of your Raspberry Pi and the operating system you are using. It's recommended to refer to the official documentation or community forums for more specific instructions tailored to your setup.