fred-graphene tried redownloading it from the play store and it shows as "This app won't work for your device"
Google Play isn't listing the app because GrapheneOS doesn't "pass" Play Integrity. In other words, GrapheneOS isn't "certified" by Google.
You can try contacting the app developers / customer support to see if they can list the app. In the meantime, you can install the app with Aurora. The project doesn't advise people to use Aurora if an app can be downloaded from the Play Store. In these sorts of cases, I'd say Aurora is the least bad way to download and install the app.