Yosemite (10.10) and Earlier
A display bug with showing and hiding files in an Open or Save dialog box means that the keyboard shortcut doesn’t work in the Finder’s Column view mode in macOS Yosemite and earlier. The remaining Finder views (icon, list, cover flow) work fine for displaying hidden files.
El Capitan (10.11) and Later
The keyboard shortcut for showing hidden files in Open and Save dialog boxes works fine in El Capitan and later versions of macOS. However, there’s one additional detail. Some Open and Save dialog boxes don’t display all the icons for the Finder views in the dialog box toolbar. If you need to change to a different Finder view, try selecting the Sidebar icon (first one on the left) in the toolbar. This toggle should cause all the Finder view icons to become available.
The Invisible File Attribute
Using the Open or Save dialog box to view hidden files does not change the files’ invisible attribute. You cannot use this keyboard shortcut to save a visible file as an invisible one, nor can you open an invisible file and then save it as a visible one. Whatever the files’ visibility attribute was set to when you started working with the file is how the file remains.
