/etc/xdg/autostart/ is in cinnamon-settings-daemon 3.6.2-1.
This file is owned by root:root, with mode 0o755.
..
/etc/xdg/autostart/cinnamon-settings-daemon-a11y-keyboard.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-a11y-settings.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-automount.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-background.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-clipboard.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-color.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-cursor.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-housekeeping.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-keyboard.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-media-keys.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-mouse.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-orientation.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-power.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-print-notifications.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-screensaver-proxy.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-smartcard.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-sound.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-xrandr.desktop
/etc/xdg/autostart/cinnamon-settings-daemon-xsettings.desktop