Ctrl
+Shift
+S
is indeed listed in Tools
>Customize
, Keyboard
tab.
You must be aware there are two lists of shortcuts selected by the radio buttons in the dialog.
-
application-specific shortcuts with the lower radio button (selected by default when you open the dialog)
This set depends on whether you opened the dialog in Writer, Calc, Impress, Draw, Base or Math. These shortcuts will only be effective in said component (application)
-
global shortcuts common to all components with the upper radio button labeled LibreOffice
Ctrl
+Shift
+S
is one of them.
The application specific list has precedence over the global one. The shortcut is first looked for in the app-list and, if not found, in the global list.
This is why it is still displayed for File
>Save As
. A bit confusing if you don’t know about the two lists.
To show the community your question has been answered, click the ✓ next to the correct answer, and “upvote” by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!