missing 'show desktop' widget on taskbar

[babag]

i've always used a 'show desktop' icon on my taskbar but, after a recent reinstall of ubuntu studio 18.04 and kde, followed by an update, it seems to have gone missing. when i r-click the taskbar to add the widget, it no longer appears anywhere in the widgets list. there is a win7 show desktop widget but that doesn't seem to install properly. i've tried several times in different ways but it never appears on the taskbar. does anyone have any suggestions as to how to get a 'show desktop' icon back?

thanks,
babag