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.
Nope. I used that feature just today to add another account. Works on my iPhone X.
Also, the last commit to the app was a year ago, if you head to their github page.
Reading / using existing codes might work properly, or manually inputting them.