Context Menus in Nautilus (Ubuntu 18.04)

Confirmed, clicking between the files should work in 18.04. Just make sure you right-click between the icons, not on the text below the icons. I'll try to get a screenshot.

Unfortunately, the screenshot seems to miss the context menu for some reason: perhaps because I was just capturing the current window. But where you see the pointer is where you need to right click to get the context menu.

Edit:

Alternatively, if you are in the list view and you have a right click key on your keyboard, you can simply hit that key on your keyboard directly after first opening the folder (no files yet selected). If there is a file selected, Ctrl+Space will unselect it.