The problem with custom ROMs is that a lot of banking apps try to detect if the phone's bootloader is unlocked or it's rooted, and these apps then refuse to work. There are workarounds but they're not bulletproof.
Pixels have relockable bootloaders, so banking apps can run on CalyxOS (and, maybe, GrapheneOS)
This is just not true. I've been using my banking apps succesfully since last year across 3 rooted cheap phones with 4 distinct custom LineageOS ROMs with just some Magisk modules.