python3-pyqt6 depends on qt6-base-abi. I believe this is meant to be supplied as a virtual package by libqt6core6t64, however installing python3-pyqt6 still fails even with libqt6core6t64 installed first.
As a dependency, the libqt6core6t64 entry is present in Xubuntu (left) but missing in KDE Neon (right):
How should I proceed? Should I file a bug report?