Star Wars: Imperial Assault using the app

Star Wars: Imperial Assault was recently recommended to me, and I have some questions. My partner and I finished all the Gloomhaven games, as well as Descent, and really like the tactical, turn-based 'dungeon crawler' feel. We're working on Pericle at the moment (tough sledding, but we're getting there). We enjoy the DnD 'feel' of games, but don't want to deal with a GM.

What I can't figure out is how the app works with SW:IA. I've watched a couple of Youtube videos to get a feel for the game, but no one seems to be using the app. My partner and I really like app-based games, so this would be a huge benefit (and we only want a fully co-op experience). Is there an option to play without the app, or with the app?

Also, it seems this game was published over 10 years ago, so perhaps the app was added later in some expansions? I realize I am very late to the game on this, so please help me catch up.