Maybe this one https://packages.ubuntu.com/focal/qt5-default with it's dependencies or just https://packages.ubuntu.com/focal/qtbase5-dev .
IIRC some development packages containing headers aren't available by the regular repositories with the suffix -dev, instead they are available by another source with another suffix. On the quick I couldn't find any pointer by the Ubuntu wiki, the Ubuntu help or by launchpad. -- xubuntu-users mailing list [email protected] Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/xubuntu-users
