After stumbling across how to do this, then losing it and only after a long search finally re-discovering this little documented feature, I've decided it's likely worth posting.
Basic Concept of Hidden Files in Unix
In Linux filesystems, anything with a leading period (files or folders) is considered to be hidden and viewable only with an "all" option using whatever utility to list the files. Unfortunately, this may not be sufficient to clear the clutter in today's world.
KDE enhanced hidden file support, Why
As a Desktop that sits on top of Linux, KDE supports the basicLinux hidden files/folders convention using the leading period in applications like File Managers (eg Dolphin).
But, what about other files? An example of another file type a User won't likely want to list is the backup file that is created with a trailing tilde (~) whenever a document is modified. This would especially be true if files are dropped into the Folderview widget on the KDE Plasma Desktop, potentially up to half of all the space would be occupied by these undesirable files.
In KDE, you can now hide any definable filetype, re-claiming space and making file/folder listing more efficient.
KDE enhanced hidden file support, How
This feature seems to be hidden in a corner and not configurable in any main file management tool like Dolphin or the KDE management utilities and so far I haven't found it in Google, the KDE website or any other place.
It's only configurable in the KDE Folder Widget properties.
First, unlock widgets on your Desktop if necessary (Is unlocked by default).
1. Either rt-click in the open space of an existing Folder View Widget or add a new Widget to your desktop by
Rt-click desktop > Add Widgets > Folder View Widget (Drag to Desktop) > rt-click on empty space in new Folder View Widget >
2. After rt-clicking on the Folder View Widget, select Folder View Settings
3. Modify Location to point to one of the three location types... The Desktop folder itself, a pre-configured (by KDE) "Place" or a custom folder of your choice. The first choice is OK if you don't already have something else in mind and you just need one Folder View.
4. In the Navigation Pane on the left, click on "Filter."
5. In the top dropdown, select "Hide Files Matching"
6. In the bottom "File Types" input box (Not the middle box), type your pattern in my example the tilde (~), and you will see the backup file type already defined.
7. Make sure the backup file type is checked, and click "OK" which saves changes and closes the Folder Settings window.
8. Check your nandiwork. Drop a new file if needed into the Folder View Widget, modify the contents and save. Open your KDE File manager to the location of your Folder View Widget and list the contents. In both cases you should not see your backup files unless you select the option to view hidden files.
When you've finished modifying your Desktop's widgets, don't forget to lock the widgets to guard against accidental loss.