GrapheneOS already has their own attestation API that verifies the app is running on GrapheneOS. Since GrapheneOS is more secure than stock Android, security conscious apps like banking apps have a solid technical reason to use the API and support Graphene.

We just need to raise the profile of GrapheneOS and convince more banking apps to use this API, if they are already using Google's attestation API.

GrapheneOS's strategy for raising their profile and being seen as more legitimate is that they've formed a partnership with Motorola Mobility, who will be manufacturing Graphene compatible phones. <https://motorolanews.com/motorola-three-new-b2b-solutions-at...>