/usr/share/applications/screensavers/fadeplot.desktop is in xscreensaver-data-extra 5.34-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Name=FadePlot
Exec=/usr/lib/xscreensaver/fadeplot -root
TryExec=/usr/lib/xscreensaver/fadeplot
Comment=Draws what looks like a waving ribbon following a sinusoidal path. Written by Bas van Gaalen and Charles Vidal.
StartupNotify=false
Terminal=false
Type=Application
Categories=Screensaver;
OnlyShowIn=MATE;
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