Getting "model not found" since updating Jupyter to 3.x

[orome]

Describe the issue

Any plot creation using Matplotlib results in Error displaying widget: model not found

Versions

 3.9.1 (default, Dec 24 2020, 16:23:16) 
[Clang 12.0.0 (clang-1200.0.32.28)]
ipympl version: 0.5.8
jupyter core     : 4.7.0
jupyter-notebook : 6.1.6
qtconsole        : 5.0.1
ipython          : 7.19.0
ipykernel        : 5.4.2
jupyter client   : 6.1.7
jupyter lab      : 3.0.0
nbconvert        : 6.0.7
ipywidgets       : 7.6.2
nbformat         : 5.0.8
traitlets        : 5.0.5
Known nbextensions:
  config dir: /Users/Rax/.jupyter/nbconfig
    notebook section
      nbdime/index  enabled 
      - Validating: OK
  config dir: /Users/Rax/Documents/Projects/Coding/Python/venvs/dataviz/etc/jupyter/nbconfig
    notebook section
      jupyter-matplotlib/extension  enabled 
      - Validating: OK
      nbdime/index  enabled 
      - Validating: OK
      jupyter-js-widgets/extension  enabled 
      - Validating: OK
  config dir: /usr/local/etc/jupyter/nbconfig
    notebook section
      jupyter-matplotlib/extension  enabled 
      - Validating: OK
      nbdime/index  enabled 
      - Validating: OK
      jupyter-js-widgets/extension  enabled 
      - Validating: OK
JupyterLab v3.0.0
/Users/Rax/Documents/Projects/Coding/Python/venvs/dataviz/share/jupyter/labextensions
        @jupyter-widgets/jupyterlab-manager v3.0.0 enabled OK (python, jupyterlab_widgets)

Other labextensions (built into JupyterLab)
   app dir: /Users/Rax/Documents/Projects/Coding/Python/venvs/dataviz/share/jupyter/lab
        @jupyterlab/git v0.23.3 enabled  X
        @kiteco/jupyterlab-kite v1.2.0 enabled OK
        jupyter-matplotlib v0.7.4 enabled OK
        nbdime-jupyterlab v2.0.1 enabled  X

   The following extension are outdated:
        @jupyterlab/git
        nbdime-jupyterlab
        
   Consider running "jupyter labextension update --all" to check for updates.

[martinRenou]

Ipympl does not support JupyterLab 3 yet. Leaving this issue open for others to see it. It should be updated soonish.

[snickell]

For anyone else looking in the future, this will be fixed by #272

[ianhi]

@snickell see also #272 (comment)

[GF-Huang]

hehe, take me a long time to install nodejs, then tell me not supports 3.x?