The following packages have unmet dependencies: qt5-default : Depends: qtbase5-dev but it is not going to be installed

This error usually occurs when there are missing or conflicting dependencies for the package you are trying to install. In this case, it seems that the package "qt5-default" depends on the package "qtbase5-dev", but it is not available for installation.

To resolve this issue, you can try the following steps:

1. Update package lists: Run the following command to update the package lists on your system:

   sudo apt update

2. Fix broken dependencies: Run the following command to fix any broken dependencies:

   sudo apt --fix-broken install

3. Install required packages: Try to install the required packages explicitly using the following command:

   sudo apt install qtbase5-dev

If the above steps don't resolve the issue, it might be helpful to provide more information about your system, such as the operating system and version you are using, and any other relevant details.