Missing remove duplicates

I can' t see a remove duplicates command in any of the folder menus as shown in the 
manual.

I've looked in the plugins but can't see anything obvious, and a few   internet searches 
imply remove duplicates comes as standard.

Ctrl + * is enabled in the keyboard shortcuts, but doesn't appear to have any visible effect.

I'm running 5.13.3 (19.12.3) under Kubuntu
KDE Frameworks 5.68.0
Qt 5.12.8 (built against 5.12.8)
The /xcb/ windowing system.
I'm running the same version on another machine, which also has no remove duplicates 
folder menu entry. 

Any  thoughts would be appreciated.


Regards
Tony Bazeley

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