pip freeze > requirements.txt adds all globally installed packages to requirements.txt

Hi, I'm a new user of PyCharm. I created a project for this course in PyCharm and it created the virtual environment to go along with the project automatically. When I went to create the requirements.txt file for this virtual environment, it listed a lot of packages—I'm assuming they were all the packages installed globally on my machine. It may also be relevant to note that when I went to install sqlalchemy in this virtual environment, it said it was already installed.

I deleted the virtual environment created by PyCharm and created a new one, installed sqlalchemy with pip, and then pip freeze > requirements.txt only shows sqlalchemy and typing_extensions (don't know what that is but assuming maybe a dependency of sqlalchemy?), so that seems to have solved the problem of including all my global packages.

I'm just wondering if anyone here knows what was going on and how I can avoid that in the future if I want to be able to use the virtual environments that PyCharm creates with the projects?