Anyway, I found a desktop file, put in autostart and it works.
There is however, a tiny issue. Whenever it starts, Plasma shows a desktop notification with voice signal (the same as error…). This also happens when launching the app from terminal, so the problem is with the app itself. If it is meant to be used as autostart in background, it shouldn’t have so obnoxious notification. It’s super annoying.
Is there a way to block such notification in Plasma? Or is this a situation where we must contact the devs to fix it?