Matplotlib error on Raspberry

On my Rapberry Pi Model3 is installed by default python 3.9.2 I've correctly installed :

• matplotlib 3.6.3
• numpy 1.24.1

If I create a simple .py file like this:

import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots()  # Create a figure containing a single axes.

I receive this error:

Traceback (most recent call last):
  File "/home/pi/Desktop/test.py", line 31, in <module>
    fig = plt.figure(figsize=(5,3)) # start figure
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/_api/deprecation.py", line 454, in wrapper
    return func(*args, **kwargs)
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/pyplot.py", line 783, in figure
    manager = new_figure_manager(
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/pyplot.py", line 358, in new_figure_manager
    _warn_if_gui_out_of_main_thread()
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/pyplot.py", line 336, in _warn_if_gui_out_of_main_thread
    if _get_required_interactive_framework(_get_backend_mod()):
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/pyplot.py", line 207, in _get_backend_mod
    switch_backend(dict.__getitem__(rcParams, "backend"))
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/pyplot.py", line 265, in switch_backend
    backend_mod = importlib.import_module(
  File "/usr/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/backends/backend_qt5agg.py", line 7, in <module>
    from .backend_qtagg import (    # noqa: F401, E402 # pylint: disable=W0611
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/backends/backend_qtagg.py", line 9, in <module>
    from .qt_compat import QT_API, _enum, _setDevicePixelRatio
  File "/home/pi/mytest/lib/python3.9/site-packages/matplotlib/backends/qt_compat.py", line 137, in <module>
    raise ImportError(
ImportError: Failed to import any of the following Qt binding modules: PyQt6, PySide6, PyQt5, PySide2

Any idea? Thanks in advance.