isort using your preferred Python package manager:
pip3 install isort
poetry add isort
pipenv install isort
For a fully isolated user installation you can use pipx
pipx install isort
If you want isort to act as a linter for projects, it probably makes since to add isort as an explicit development dependency for each project that uses it. If, on the other hand, you are an individual developer simply using isort as a personal tool to clean up your own commits, a global or user level installation makes sense. Both are seamlessly supported on a single machine.