Aurora Store is an alternative app store that lets you download apps directly from Google Play, but without using a Google account.
The connection to GrapheneOS is that many GrapheneOS users want apps from the Play Store, but at the same time do not want a Google account and full Google integration on their phone. That’s why Aurora Store is a popular tool:
GrapheneOS can run completely without Google apps.
Aurora Store still makes it possible to download apps from the Play Store.
However: apps that require Google Play Services or “integrity checks” (like in the message you received) may still fail, even if they are downloaded via Aurora.
At Bulder, we do not officially support GrapheneOS.
Several of our features are based on Google Play’s integrity checks, and therefore we cannot guarantee that these will continue to work as expected in the future.
There may be changes that affect the integrity check. If you experience problems, you are welcome to contact us, but please be aware that we do not provide official support for GrapheneOS.