It is never made clear that an app is required either. Often devices have an app but you don't need it at all since it was just slapped on as a feature checkbox.

I recently got a pair of Bose QC 35 headphones and out of the box they are non functional until connected to the app. I had to borrow a phone to connect them to the app to set up and then thankfully they started working on my own devices with bt and wired without needing an app.

Headphones should just work out of the box. The only useful function the app provides is firmware updates and a way to map the button to NC level.