Nopesef It is unfortunate indeed. If you press 'More info' it will take you to this screen
https://www.service.nsw.gov.au/non-standard-software which gives more details. GrapheneOS is not Google Certified in Play Protect.
The only suggestion I have really is to contact the app developers and suggest that they follow this guide instead: https://grapheneos.org/articles/attestation-compatibility-guide. It's a long shot, but might be worth a try.