by dragging the Preview folder above from the Lister Left with the right mouse button to the htdocs directory in Lister Right, then context menu: Create Hard link here.
Opus can create all the things discussed on that page. (The manual wouldn't spend time detailing things Opus can't do, after all.)
Using the DOS mklink command isn't a good idea as you won't get feedback on errors.
See the Copy command's MAKELINK argument for the syntax to doing it using an Opus command. You just need to change "hardlink" to "junction" in the command you've already added for creating hardlinks. (That command is not in any context menu by default, so it must be something you added yourself. The command to create junctions is almost the same, just one word different, so it should be easy to set up based on what you already have.)