Hi PyQt-Qwt has finally been added to Debian. https://tracker.debian.org/pkg/pyqt-qwt
It is built on Qt5 and Qwt6. Since Python2 will soon be obsolete in Debian, the Debian package only supports Python3. It is easy to upgrade existing programs that use PyQwt5 to using PyQt-Qwt. Regards Gudjon