Try enabling the per-app exploit protection compatibility mode as an initial step. This works for most banking apps which don't work with the defauilts.

GrapheneOS isn't rooted and fully preserves the standard security model along with greatly improving it. You should report this to their customer support and leave a review about it on the Play Store too. Don't include a link in the review to avoid it being spam filtered. Give their customer support a link to https://grapheneos.org/articles/attestation-compatibility-guide.