To make an application automatically start on systems with a session manager (e.g., systemd), it is enough to put its desktop file into one of the following directories:
$XDG_CONFIG_HOME/autostart/ (by default, ~/.config/autostart/)$XDG_CONFIG_DIRS/autostart/ (by default, /etc/xdg/autostart/)The desktop files in the user's directory take precedence.
On GNOME, this can be simplified via the GNOME Tweaks application that provides an app selector for startup applications.
See also: