You can always switch to US app store region (cancel exisiting subscriptions, leave family, and wait until apple music/tv subscription is expired).

You won’t be able to use non-US credit card for the app store but you can always buy US virtual apple gift cards on amazon straight from apple shop there.

I guess it’s easier to find a testflight link if one is set up, or just to create a new account altogether, and sign in to it temporarily.

Just that easy! /s