So I'm not on iOS but... the websites I need to use for various work things all require that you use a specific authenticator. But they all choose a different random one. It drives me insane. I have 4 different apps. Google Authenticator, Authy, Duo Mobile, and Onelogin Protect. I pray I change jobs before I get a new phone.
I realize there are exceptions to this, and you might fall into that category, but…
Most of the time when websites say they require a particular app, they actually don’t. Like if a website says to use Google Authenticator, you can actually use any TOTP app. There is even a workaround for using Steam’s TOTP without their app.
Don’t be scared to just try importing the QR or text based code into another app when you are signing up for a service. A functioning website won’t let you progress to the next screen without having the proper code in your app.