“Siri” (whatever it has morphed into) is a pervasive DWIM engine in iOS these days. When you do a search for an app Siri decides what to display (e.g. when I go to a certain location with a “smart” lock and pull down search, the app for that lock is always offered first, but never in other locations).

These days the voice part is just a UI mode. I use it on my watch and occasionally on my phone when I am wearing earbuds and my phone is in my pocket, but have it disabled on my Mac.