This is quite literally one of my two grievances against Ubiquiti at the moment: its intense requirement for mobile apps for initial setup.
Stop mandating apps that will eventually break or cease being supported. Give us an OOBE that can be run independent of some mobile app.
I was able to install there controller software on pretty much any PC (windows or linuix) and adopt and configure APs. No phone required. Not sure about other networking gear.
I don’t think I’ve ever _needed_ to use the Unifi mobile app. When I connect something to my network, it shows up in the Unifi controller web app ready to adopt.