What banking app specifically?
A lot of banking apps use Play Services “GMS Vision API” that is not implemented in full at the microG end. Last I checked it lacked a qrcode module - Need Google Play Services for bank app - #29 by tcecyk
See banking apps struggling: https://github.com/microg/GmsCore/issues?q=is%3Aissue+is%3Aopen+gms+vision
If you look at it with logcat you could confirm if it is indeed that class or something else. If so, it’d be up to a code contributor to microG to implement it. Google moves to MLkit for the function though, a new API for microG altogether.