I'd like to keep my current App Store account. There must be another solution ...

Where to get official support from Apple on this?

Same here - TestFlight 3.7.1 build 481.5 - iPhone SE (1st gen) / iOS 15.8.3 @Apple please fix this. Thanks.

Same here - TestFlight 3.7.1 build 481.5 - iPhone SE (1st gen) / iOS 15.8.3 @Apple please fix this. Thanks.

Same here - TestFlight 3.7.1 build 481.5 - iPhone SE (1st gen) / iOS 15.8.3 @Apple please fix this. Thanks.

Issue seems to be fixed here