See googleapis/synthtool#1916

noxfile.py

@@ -182,7 +182,19 @@ def docs(session):
 
  session.install("-e", ".[tracing]")
  session.install(
- "sphinx==4.0.1", "alabaster", "recommonmark", "django==2.2"
+ # We need to pin to specific versions of the `sphinxcontrib-*` packages
+ # which still support sphinx 4.x.
+ # See https://github.com/googleapis/sphinx-docfx-yaml/issues/344
+ # and https://github.com/googleapis/sphinx-docfx-yaml/issues/345.
+ "sphinxcontrib-applehelp==1.0.4",
+ "sphinxcontrib-devhelp==1.0.2",
+ "sphinxcontrib-htmlhelp==2.0.1",
+ "sphinxcontrib-qthelp==1.0.3",
+ "sphinxcontrib-serializinghtml==1.1.5",
+ "sphinx==4.5.0",
+ "alabaster",
+ "recommonmark",
+ "django==2.2"
  )
 
  shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
@@ -207,6 +219,15 @@ def docfx(session):
 
  session.install("-e", ".[tracing]")
  session.install(
+ # We need to pin to specific versions of the `sphinxcontrib-*` packages
+ # which still support sphinx 4.x.
+ # See https://github.com/googleapis/sphinx-docfx-yaml/issues/344
+ # and https://github.com/googleapis/sphinx-docfx-yaml/issues/345.
+ "sphinxcontrib-applehelp==1.0.4",
+ "sphinxcontrib-devhelp==1.0.2",
+ "sphinxcontrib-htmlhelp==2.0.1",
+ "sphinxcontrib-qthelp==1.0.3",
+ "sphinxcontrib-serializinghtml==1.1.5",
  "gcp-sphinx-docfx-yaml",
  "alabaster",
  "recommonmark",