Try the "scan code" button which should activate the camera and the app will crash. I just tested it with my iPhone and verified. The iOS App Store application was last updated 4 years ago. There's also comments there saying it doesn't work anymore.
Reading / using existing codes might work properly, or manually inputting them.
Interestingly my wife's XS is having the problem you describe but not my X.
I've sent a note to the maintainers, but there's an open git issue for it. Not sure when their commits will roll to the store.
I'm told by multiple colleagues at redhat that they've raised this with internal support, so it should be sorted eventually. Lots of iphones in redhat and this is the app they officially support for TFA internally.
Reading / using existing codes might work properly, or manually inputting them.