Cannot use SageMath notebooks

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I am having trouble using SageMath notebook. I think it all started when I was installing NbExtensions, while in the process of installing the dependency lxml which crashed. I got a full screen of red paths, errors and swearing. I think the installation is half-baked and is causing troubles.

The last bit of text from the notebook server reads:

Or copy and paste one of these URLs:
        http://localhost:8888/?token=4a562cc05a523f2f9ecb292097aaffb56ff5b5fba55512b7
     or http://127.0.0.1:8888/?token=4a562cc05a523f2f9ecb292097aaffb56ff5b5fba55512b7
[I 00:15:33.632 NotebookApp] Creating new notebook in
[W 00:15:41.059 NotebookApp] 404 GET /nbextensions/jupyter_jsmol/extension.js?v=20211001001508 (127.0.0.1) 54.35ms referer=http://localhost:8888/notebooks/Untitled8.ipynb?kernel_name=sagemath

after which the notebook server closes silently on its own and very quickly.

I have just installed SageMath 9.3 for Windows. I have uninstalled it and reinstalled it, while trying to delete folders such as .sage, restarting the PC to make a clean install. I think I touched all the usual troubleshooting bases.

I would appreciate some guidance as I regularly use these workbooks and I have no clue how to go about it.