As I’ve mentioned in the past, my organization is behind an intranet. So sometimes all we have is the source repo of a Visual Studio Code extension. These have a .vsixmanifest in the root folder and an
extensions/package.json file. And I had struggled a bit with installing these easily.
The first option is to package the extensions. Just zip the folder and rename the archive to .vsix, then you can install it under
Extensions > ... > Install from VSIX....
The second option, which I recommend, is simply copy/pasting the folder as-is into
C:\Users\[user]\extensions in Windows, a.k.a
%USERPROFILE%\extensions), then reload VS Code.