Actually the process is described differently in this comment:
You should do something along the liens of
# %%
# Do the actual plotting
connectivity_fig = plot_sensors_connectivity(
epochs.info,
con.get_data(output='dense')[:, :, 0]
)
# Take a screenshot of the 3D scene
screenshot = connectivity_fig.plotter.screenshot()
# The screenshot is just a NumPy array, so we can display it via imshow()
# and then save it to a file.
fig, ax = plt.subplots(figsize=(10, 10))
ax.imshow(screenshot, origin='upper')
ax.set_axis_off() # Disable axis labels and ticks
fig.tight_layout()
fig.savefig('connectivity.png', dpi=150)
Not sure if this will fix the issue you described above, though!
You may want to consider not using the Notebook 3d backend by first running:
mne.viz.set_3d_backend("pyistaqt")
Richard