Yuh, which once was owned by both Postfinance and Swissquote, works without Play Integrity. Support for GrapheneOS is confirmed - see https://github.com/PrivSec-dev/banking-apps-compat-report/is...
The real issue is that most "legacy" banks have to comply with stupid regulations that force them to come up with these stupid solutions.
Banks are lazy and find the quickest way to comply with said regulations - simply by enabling Google Play Integrity.
About the whole US thingie - yes, that's true, and it's what happens if you get sanctioned. I'm pretty sure russians (and other people from sanctioned countries) have similar limitations elsewhere. In Switzerland US nationals have huge problems in opening accounts because of the whole bank secrecy law that allowed many americans to hide money from the IRS in Switzerland.