If you want to install a package into your specific virtual environment, you need to first "activate" that environment. Likewise, if you want to run your script in that environment, you need to first "activate" it. You can do this manually or preferably let VSCode handle it for you.

In order to tell VSCode(especially the language server which is pylance) to use that environment:

1. Open up your Command Palette(press ctrl+shift+P or f1) and type : "python: select interpreter".
2. Browse/Select your newly created python interpreter's path inside your venv.
3. Add "python.terminal.activateEnvironment": true to your setting.json file(It's also possible via GUI setting of course by searching for python: activate environment). This will automatically detect and activate your venv whenever you open your integrated terminal. Obviously If the path should points to a venv interpreter. (Note: you have to have a Python file opened in your editor).

You can also set your Python's interpreter path manually:

1. Create a folder called .vscode in your workspace.
2. Create a file called settings.json inside it.
3. Add these to settings.json:

{
    "python.defaultInterpreterPath": "PATH_TO_VENV_INTERPRETER",
    "python.terminal.activateEnvironment": true
}

Note: What I normally do is, I insert a "python.defaultInterpreterPath" key to my User settings.json which points to my global interpreter. Then I create Workspace settings.json for each of my projects and add the same key which points to my venv's interpreter. Remember, workspace settings.json will overwrite user's settings.json.

This way whenever you open VSCode in a project folder it automatically knows it should activate your venv's interpreter(I told it to do so with "python.terminal.activateEnvironment") and if you open VSCode in a normal folder it correctly use your global's interpreter.

Difference between User and Workspace settings.json.

Hint: The original question is about VsCode but this answer is about VsCodium.

a) In VsCodium, Pylance is not shown as extension by default. As a hack, one could adapt the extensionsGallery settings to show and install Pylance:

In VSCodium\resources\app\product.json

set

"extensionsGallery": {
    "serviceUrl": "https://marketplace.visualstudio.com/_apis/public/gallery",
    "cacheUrl": "https://vscode.blob.core.windows.net/gallery/index",
    "itemUrl": "https://marketplace.visualstudio.com/items"
},

Source:

https://github.com/VSCodium/vscodium/discussions/1641

However, that might not be compatible with the license terms of pylance.

b) If Pylance does not work, try basedpyright as an alternative extension (open source instead of closed source):

c) Or switch to the Jedi Language server in VsCodium settings.

https://github.com/detachhead/basedpyright/

I found this link that informs us that we should add an extra path.

These extra roots must be specified to the language server. The easiest way to do this (with the VS Code Python extension) is to create a workspace configuration which sets python.analysis.extraPaths. For example, if a project uses a sources directory, then create a file .vscode / settings.json in the workspace with the contents:

{
     "python.analysis.extraPaths": ["./sources"]
}

https://github.com/microsoft/pylance-release/blob/master/TROUBLESHOOTING.md#unresolved-import-warnings

Change the setting: python.languageServer