Unable to convert notebook to Markdown ("ModuleNotFoundError"; macOS)

[perwin]

I'm having a problem running nbconvert (at least when I try converting a Jupyter notebookk to markdown format). It has always worked just fine on my system, but when I tried using it a week ago (after not using it for several months), I get the following:

% jupyter nbconvert --to markdown pyimfit_emcee.ipynb
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.11/bin/jupyter-nbconvert", line 5, in
from nbconvert.nbconvertapp import main
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/nbconvert/nbconvertapp.py", line 193, in
class NbConvertApp(JupyterApp):
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/nbconvert/nbconvertapp.py", line 252, in NbConvertApp
Options include {get_export_names()}.
^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/nbconvert/exporters/base.py", line 145, in get_export_names
e = get_exporter(exporter_name)(config=config)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/nbconvert/exporters/base.py", line 106, in get_exporter
exporter = items[0].load()
^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/metadata/init.py", line 202, in load
module = import_module(match.group('module'))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/importlib/init.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/jupyter_contrib_nbextensions/init.py", line 5, in
import jupyter_nbextensions_configurator
File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/jupyter_nbextensions_configurator/init.py", line 18, in
from notebook.base.handlers import APIHandler, IPythonHandler
ModuleNotFoundError: No module named 'notebook.base.handlers'

This is the setup:
System: MacBook Pro (15-inch, 2019), macOS 13.6.4
Python 3.11.4 (python.org install)

% jupyter --version
Selected Jupyter core packages...
IPython : 8.22.1
ipykernel : 6.29.2
ipywidgets : 8.1.2
jupyter_client : 8.6.0
jupyter_core : 5.7.1
jupyter_server : 2.12.5
jupyterlab : 4.1.2
nbclient : 0.9.0
nbconvert : 7.16.1
nbformat : 5.9.2
notebook : 7.1.0
qtconsole : 5.5.1
traitlets : 5.14.1

I can get the same file to convert properly on a different laptop, where the setup and versions are:

System: MacBook Pro (13-inch M1 Pro, 2021), macOS 13.6.2
Python 3.11.4 (python.org install)

% jupyter --version
Selected Jupyter core packages...
IPython : 8.16.1
ipykernel : 6.27.2
ipywidgets : 8.1.1
jupyter_client : 8.6.0
jupyter_core : 5.5.0
jupyter_server : 2.11.0
jupyterlab : 4.0.9
nbclient : 0.8.0
nbconvert : 7.9.2
nbformat : 5.9.2
notebook : 7.0.6
qtconsole : 5.4.0
traitlets : 5.8.1