@spiritedaway @Bondrewd It depends on what you mean by 'modified non standard' and 'stock Android', but banking apps will generally work on a number of custom Android distributions providing they aren't rooted.
All of my (UK-based) banking apps work on Calyx, for example.
@spiritedaway Yep — if you want it to. On initial install you choose the level of integration you want microG to support, as detailed here: https://calyxos.org/docs/guide/microg/