SUMMARY IIRC it used to be possible to interactively create softlinks for files and folders. Now this option seems to be missing and the only alternative is a very restricted custom extension or using the command line, which is both not very convenient. ADDITIONAL INFORMATION
You can already create a softlink by drag and drop-ing a file or folder while holding ctrl and shift. I do think this should be shown more clearly, IIRC it used to be shown alongside "copy here" and "move here" when you drag and dropped without holding anything, which is what taught me the shortcut. I'm not sure why it was removed, it seemed like the best place to show that shortcut.
It's in the context menu of the default drag.