Extension "sphinx.ext.todo" and epub: NotImplementedError

[Murmele]

Describe the bug

Trying to build epub files

How to Reproduce

Steps to reproduce:

1. Create sphinx project with sphinx.ext.todo extension
2. Add a todo to the file .. todo:: add a description
3. Build: sphinx-build -M epub "source" "build" -v -E

Observed

NotImplementedError: <class 'sphinx.writers.html5.HTML5Translator'> departing unknown node type: todo_node

Environment Information

[tool.poetry]
name = "sphinx_debug"
version = "0.1.0"
description = ""
authors = ["Author"]

[tool.poetry.dependencies]
python = "^3.11"
sphinx = "^8.1.3"
sphinx-rtd-theme = "^3.0.2"
sphinxcontrib-youtube = "^1.4.1"


[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

Sphinx extensions

["sphinx.ext.todo"]

Additional context

# Platform:         win32; (Windows-10-10.0.22621-SP0)
# Sphinx version:   6.2.1
# Python version:   3.10.10 (CPython)
# Docutils version: 0.18.1
# Jinja2 version:   3.1.2
# Pygments version: 2.15.1

# Last messages:
#   done
#   preparing documents...
#   done
#   writing output... [  1%] 2D_plotting
#   writing output... [  3%] 2D_plotting/2D_plotting_boxplot
#   writing output... [  5%] 2D_plotting/2D_plotting_histogram
#   writing output... [  7%] 2D_plotting/2D_plotting_xycurve
#   writing output... [  9%] 2D_plotting/2D_plotting_xycurve_formula
#   writing output... [ 11%] 404
#   writing output... [ 12%] computational_notebooks

# Loaded extensions:
#   sphinx.ext.mathjax (6.2.1)
#   alabaster (0.7.13)
#   sphinxcontrib.applehelp (1.0.4)
#   sphinxcontrib.devhelp (1.0.2)
#   sphinxcontrib.htmlhelp (2.0.1)
#   sphinxcontrib.serializinghtml (1.1.5)
#   sphinxcontrib.qthelp (1.0.3)
#   sphinxcontrib.jquery (4.1)
#   sphinx_rtd_theme (unknown version)
#   sphinxcontrib.youtube (1.4.1)
#   sphinx.ext.todo (6.2.1)

# Traceback:
Traceback (most recent call last):
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\cmd\build.py", line 285, in build_main
    app.build(args.force_all, args.filenames)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\application.py", line 353, in build
    self.builder.build_update()
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\__init__.py", line 311, in build_update
    self.build(to_build,
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\__init__.py", line 378, in build
    self.write(docnames, list(updated_docnames), method)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\__init__.py", line 586, in write
    self._write_serial(sorted(docnames))
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\__init__.py", line 596, in _write_serial
    self.write_doc(docname, doctree)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\_epub_base.py", line 371, in write_doc
    super().write_doc(docname, doctree)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\builders\html\__init__.py", line 666, in write_doc
    self.docwriter.write(doctree, destination)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\writers\__init__.py", line 78, in write
    self.translate()
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\writers\html.py", line 37, in translate
    self.document.walkabout(visitor)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 199, in walkabout
    if child.walkabout(visitor):
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 199, in walkabout
    if child.walkabout(visitor):
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 199, in walkabout
    if child.walkabout(visitor):
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 212, in walkabout
    visitor.dispatch_departure(self)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\sphinx\util\docutils.py", line 601, in dispatch_departure
    super().dispatch_departure(node)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 2046, in dispatch_departure
    return method(node)
  File "C:\Users\<USER>\AppData\Local\Programs\Python\Python310\lib\site-packages\docutils\nodes.py", line 2068, in unknown_departure
    raise NotImplementedError(
NotImplementedError: <class 'sphinx.writers.html5.HTML5Translator'> departing unknown node type: todo_node

[picnixz]

I cannot reproduce the issue with the latest Sphinx. Can you try with the latest version please? thanks in advance.