should be installed in the environment from which you run Jupyter Notebook or JupyterLab. This might be your base conda environment, but it need not be. For instance, if the environment notebook_env contains the notebook package, then you would run
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conda install -n notebook_env nb_conda_kernels
Any other environments you wish to access in your notebooks must have an appropriate kernel package installed. For instance, to access a Python environment, it must have the ipykernel package; e.g.
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conda install -n python_env ipykernel
To utilize an R environment, it must have the r-irkernel package; e.g.
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conda install -n r_env r-irkernel
For other languages, their corresponding kernels must be installed.