100% sure that all decent banking app use device fingerprinting. 100% sure that it is not breaking the rules and it is really important that they keep doing it.
Do they really? [Citation needed] very much here. Which fintech app fingerprints devices? What would even be the point of doing that. You can persist a token in the keychain for that which is enough unless you are devious.
Fingerprinting is a form of 2 factor authentication, it's easy to perform and it's relatively efficient against fraud.
The first time you use an app you have to enter your user name and password and that is stored in the secure enclave that not even the operating system had access to.
When the banking app request validation, you use your fingerprint to authenticate and the secure enclave sends the username and password to the app. The fingerprint scanner is connected directly to the secure enclave.
When you sell your phone, you go through the process of erasing your phone, the encryption key is destroyed and your fingerprint is no longer valid.