At the moment Jupytext requires nbformat<=5.0.8

.github/workflows/continuous-integration.yml

@@ -191,7 +191,7 @@ jobs:
           run: |
             python -m pip install --upgrade pip
             # All dependencies but markdown-it-py
-            pip install nbformat pyyaml toml
+            pip install 'nbformat<=5.0.8' pyyaml toml
             pip install -r requirements-dev.txt
         - name: Install a Jupyter Kernel
           run: python -m ipykernel install --name python_kernel --user

environment-ci.yml

@@ -9,6 +9,7 @@ dependencies:
   - jupyter
   - ipykernel
   - nbconvert
+  - nbformat<=5.0.8
   - pyyaml
   - toml
   - pip

environment.yml

@@ -4,8 +4,8 @@ channels:
   - conda-forge
 dependencies:
   - python>=3.6
-  - jupyter
   - jupyterlab>=3.0
+  - nbformat<=5.0.8
   - jupyter-packaging
   - pyyaml
   - toml

requirements.txt

@@ -1,4 +1,4 @@
-nbformat>=4.0.0
+nbformat>=4.0.0,<=5.0.8
 pyyaml
 toml
 markdown-it-py~=0.6.0