We noticed this was broken in a previous version of iOS 15, I think it started with iOS 15.0 or 15.1. However, as of iOS 15.2, this has been corrected, and in-line URLs (those not embedding the link behind some text) on the Back Fields of Apple Wallet are once-again hyperlinked properly. The same thing happened with phone numbers at the same time, but as of 15.2, those are also fixed (aka, clickable) once again.