NBExtensions tab loads no extensions, /nbextensions returns 404 page not found when Classic Notebook launched from JupyterLab

I am running a Jupyter server on TKGI using Docker. I have run the following commands in JupyterLab terminal to enable nbextensions in Jupyter Notebook:

$ pip install jupyter_nbextensions_configurator

$ jupyter nbextension install --sys-prefix --py jupyter_nbextensions_configurator --overwrite

$ jupyter nbextension enable --sys-prefix --py jupyter_nbextensions_configurator

$ jupyter serverextension enable --sys-prefix --py jupyter_nbextensions_configurator

$ jupyter contrib nbextensions install

These return no errors, however the nbextensions tab just shows a loading screen and /nbextensions does not exist. How can I fix this? I’ve looked through countless github, stackoverflow, and jupyter discourse threads however none of the suggested fixes have worked.

EDIT: I have seen suggestions on other threads to run the following command
jupyter nbextensions_configurator enable --user

However this results in “Jupyter command jupyter-nbextensions_configurator not found.”