Upstream decided to move to PySide6 instead of PyQt6. You can see the pull request introducing PySide6 at https://github.com/vectorgraphics/asymptote/pull/550
You are right with the python3-pyside6, which you can just drop. python3-pyside6.qtsvg depends on *qtcore, *qtgui, and *qtwidgets, which provide the necessary files.
