This is very common and more or less happens every year with the new OS betas. Best guess is they lock the system version to prevent tampering.
Not likely to be something on Apple's side. The developers need to update their apps.
In my experience it hasn't been an issue for banking apps to do that. After all they have a couple months to do that. I, like Apple, recommend not installing the beta on your primary device due to issues like these.
Topic:
Community
SubTopic:
Apple Developers