Bug summary

I tried to pickle figures with subfigures nested.
Returns error with the following code.

Code for reproduction

#!/usr/bin/env python3
import pickle
import matplotlib.pyplot as plt

fig = plt.figure()
subfigs = fig.subfigures(2,2)
with open('fig.p', 'wb') as file:
    pickle.dump(fig, file)

Actual outcome

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[1], line 8
      6 subfigs = fig.subfigures(2,2)
      7 with open('fig.p', 'wb') as file:
----> 8     pickle.dump(fig, file)

TypeError: cannot pickle 'FigureCanvasQTAgg' object

Expected outcome

A pickle file should be saved to the working directory.

Additional information

I know the API is still provisional but I couldn't find other reports so I decided to post.
I believe this is caused by the "subfigures" API, as skipping that line makes the script work.
It's my first time to report a issue, so I'm a bit worried if I'm doing things right.

Operating system

Windows 10

Matplotlib Version

3.9.0

Matplotlib Backend

qtagg

Python version

3.12.1

Jupyter version

No response

Installation

pip