PyQt5-5.15.3 problem: "ImportError: Failed to import any qt binding"

[ullix]

Same result on Py3.6, Py3.7, Py3.8, Py3.9, running in a venv:

all works fine when using PyQt5-5.15.2, but after upgrading to 
PyQt5-5.15.3 it fails.

The traceback message is:

...
   File "/home/ullix/geigerlog/geigerlog/gsup_utils.py", line 69, in 
<module>
     import matplotlib.backends.backend_qt5agg
   File 
"/home/ullix/geigerlog/vgl39/lib/python3.9/site-packages/matplotlib/backends/backend_qt5agg.py", 
line 11, in <module>
     from .backend_qt5 import (
   File 
"/home/ullix/geigerlog/vgl39/lib/python3.9/site-packages/matplotlib/backends/backend_qt5.py", 
line 16, in <module>
     import matplotlib.backends.qt_editor.figureoptions as figureoptions
   File 
"/home/ullix/geigerlog/vgl39/lib/python3.9/site-packages/matplotlib/backends/qt_editor/figureoptions.py", 
line 11, in <module>
     from matplotlib.backends.qt_compat import QtGui
   File 
"/home/ullix/geigerlog/vgl39/lib/python3.9/site-packages/matplotlib/backends/qt_compat.py", 
line 177, in <module>
     raise ImportError("Failed to import any qt binding")
ImportError: Failed to import any qt binding


Does 5.15.3 have a known bug?

What does the error even mean, do I need to program differently?

Going back to 5.15.2 makes everything fine again.

ullix