The freedesktop specification describes how to identify file types, launch applications, and other useful desktop functions. A useful spec I’ve found recently is for launching desktop applications when you log into your machine.

In my Kubuntu 20.10 system, the directory $HOME/.config/autostart can contain .desktop files that describes the applications to start on login. Drop whichever desktop file you wish to start there. In other systems it may be located under $XDG_CONFIG_DIRS/autostart.

If you want to start up a script instead, you can put the script under $HOME/.config/autostart-scripts.