/usr/share/mate-panel/applets/ is in mate-applets-common 1.20.1-3.
This file is owned by root:root, with mode 0o755.
..
/usr/share/mate-panel/applets/org.mate.applets.AccessxStatusApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.BattstatApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.CPUFreqApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.CharpickerApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.CommandApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.DriveMountApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.GeyesApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.MateWeatherApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.MultiLoadApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.NetspeedApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.StickyNotesApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.TimerApplet.mate-panel-applet
/usr/share/mate-panel/applets/org.mate.applets.TrashApplet.mate-panel-applet