Permanently set app on launch (kiosk?)

I rooted my old Galaxy J2 today, and replaced the stock firmware with LineageOS. It works great. My next question would be to set Retroarch the first and only app on startup, which supposedly is kiosk mode, so as if the phone would basically run Retroarch as its own system. I researched a lot about this (it is called kiosk) but no clue on how to do this.