"venv" (the modern version of virtualenv) is included in python3 out of the box¹ now, so creating a virtualenv is as simple as `python3 -m venv venv`. (I usually do use one to avoid polluting the global one / I let the system package manager manage the global install.)

¹but note that Debian & Debian derivatives shove several standard library modules into individual packages, so you might need to apt-get install more than just python3.