sixtyfive only runs where it has been physically validated: a main wide camera at approximately 24mm and full Apple ProRAW support. An iPhone is added to this list after testing, never assumed from its marketing name.
Standard and non-Pro iPhones do not expose Apple ProRAW on the main camera, and older Pro models were not built with the sensor sixtyfive is calibrated against. Rather than offer a lesser camera on those phones, sixtyfive declines to run at all.
sixtyfive checks its validated device list at launch. On a phone that is not on it, the app explains exactly why, by name, instead of opening a camera it cannot stand behind.