If your using vs code on mac, it's important to have your venv installed in the same directory as your workspace.
In my case my venv was in a different directory( not in my project workspace) so a simple cut/copy-paste of my venv to the project workspace did the trick.
As soon as your venv is copied to the project workspace, your vs code will pick that up and show a notification giving you an option to select venv as an interpreter.