pyqt5/../qtdemo.py "Missing documentation"

[mjb-v9-5-2]

Error running qtdemo with pyqt5 on linux.

Command: $ python3 /usr/share/doc/pyqt5-examples/examples/qtdemo/qtdemo.py

Error message: "Could not load description. Ensure that the documentation for Qt is built".

Error message occurs when you select one of the demos.

Documentation was built with apt install of qt5-doc.

Relevant installed apps:

qt5-doc/bionic,bionic,now 5.9.5-0ubuntu1 all [installed]
pyqt5-dev-tools/bionic,now 5.10.1+dfsg-1ubuntu2 amd64 [installed]
pyqt5-examples/bionic,bionic,now 5.10.1+dfsg-1ubuntu2 all [installed]
python-pyqt5/bionic,now 5.10.1+dfsg-1ubuntu2 amd64 [installed,automatic]
python3-pyqt5/bionic,now 5.10.1+dfsg-1ubuntu2 amd64 [installed]
qt5-doc/bionic,bionic,now 5.9.5-0ubuntu1 all [installed]

System: Ubuntu 18.04.5 LTS