You need to install it from a .vsix file. You can find them here.
Download the .vsix file of the version you want. You may have to click assets to see them.
Then open VSCode, go to extensions -> click on the three dots -> install from vsix and select your file.
To install the .vsix you can also use the command

code --install-extension ms-python-release.vsix

sources :
- How can I install Visual Studio Code extensions offline?
- https://code.visualstudio.com/docs/editor/extension-gallery#_install-from-a-vsix

Thank you for reaching out. Please find the answer below.

1.Download the Visual Studio Installer: Get it from the Visual Studio download page.

2.Run the Installer with Layout Command Open Command Prompt and run on bash:  vs_installer.exe --layout C:\VSOffline --add Microsoft.VisualStudio.Workload.Python --lang en-US
This downloads all components for the Python workload. 

You can replace C:\VSOffline with your preferred path.

 
3.Select the Python Workload: During the offline setup, ensure you select the "Python development" workload which includes the Python extension.

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4.Copy the Offline Installer: After creating the offline installer, you can then transfer the entire layout folder to your offline machines for installation.

5.Install Python Interpreter: Lastly, ensure that a Python interpreter is installed either from python.org or Anaconda, as you'll need that to work with the Python extension.

Kindly refer the documentation for step-by-step guide: Create an offline installation - Visual Studio (Windows) | Microsoft Learn

If issue still persist after following all the steps, we’ll be happy to assist further if needed." Kindly mark the answer as accepted if the issue resolved".