Users often work with confidential material, which content should not bee seeable for other people. An example is when you want to show a costumer a document, want to open this via StartCenter, s/he could see content not intended for him/her. Setting a password is one, but not always a good solution. As creator you probably want to see in which document which information are as an overview/thumbnail.
A possible solution could be to create a checkbox in top of the Startcenter to choose the visibility of the below contents.
I think that there's probably an advanced setting to do what you asked.
"An advanced setting" is surely a bit too much
for an "housewife" like me or other users. ;-)
Need just a simple checkbox or some such
to hide/show documents content
(depending on password protection, of course) ad hoc.
A tooltip may warn about potential risks about this feature, when exist.
Tools -> Options -> Advanced: "Open Expert Configuration"
enter "RecentDocsThumbnail" into the Search field, and search
click the "edit" button to toggle True/False
exit & restart LibreOffice.
On restart all Thumbnail Views have been replaced by generic ODF icons.
*** This bug has been marked as a duplicate of bug 74834 ***