Python extension tries to provide project-wide IntelliSense, but that is not possible in some cases. Only Partial Intellisense via Pylance is provided in most of those cases, it means:

• Any other feature of the extension other than IntelliSense is not available.
• Extension is limited to working only with your currently opened files.
• If Jedi is explicitly selected as language server, no IntelliSense is provided.

This can happen in a few instances:

• You are working with Python code on github.dev and VS Code is running in the browser.
• You open a file from a virtual file system (such as when using the GitHub Repositories extension). Note both Jedi & Pylance are supported in this case.
• The project is currently loading. Once loading completes, you will start getting project-wide IntelliSense for it. In these cases, VS Code's IntelliSense will operate in partial mode. Partial mode tries its best to provide IntelliSense for any Python files you have open, but is limited and is not able to offer any cross-file IntelliSense features.