I have been asking various banks to support their apps on GOS officially and happy to share that Nationwide UK now plans to support it :) Or at-least that's what I got from their customer care. When banks don't support or care about it, I'm usually met with "what the hell you talking about" kinda response, so this was a welcome change.
Right now I know at-least 2 banks who officially support GrapheneOS in the sense that they are ready to work on their apps if it's broken on GrapheneOS: Starling (my favourite) and NationWide. Seems like a triumph each time I hear a response other than "what the hell ... " stuff lol.
I've put the relevant screenshots (and apologies for writing hastily and not properly/accurately explaining what GOS is etc there) in the GitHub thread about banking apps on GOS for NationWide UK: https://github.com/PrivSec-dev/banking-apps-compat-report/issues/332#issuecomment-2718750842
Next on my radar is Bank Of Scotland whose app says it's a rooted or a jailbroken device (ie. doesn't support GrapheneOS at all). Getting there slowwwwwly lol.