On a conda installation installed via -c conda-forge, trying to install nbextensions via
jupyter contrib nbextension install --user
Results in
usage: jupyter-contrib [-h] [--debug] [--generate-config] [-y] [--log-level JupyterContribApp.log_level] [--config JupyterContribApp.config_file] [extra_args [extra_args ...]]
jupyter-contrib: error: argument --user: expected one argument
Did the procedure change recently?