The Belgian ID app MyGov.be does not seem to work on grapheneOS.
I have the Google play services & Google play store installed, and I installed the app via the Google play store.
First time I tried to open it it immediately showed me an error message about a security issue on my device. Then I gave the app essentially all the permissions I could on the android app settings (sensors, internet, nearby devices, notifications and camera), and I also enabled "Exploit protection compatibility mode"
I could get a bit more into the apps registration process this time but it still always ends up showing an error message.
I don't know if this app uses the Play Integrity API or not, but it doesn't trigger the notification that I have sometimes seen GrapheneOS show when it notices that an app tries to use the API.
I'm making this thread partly to ask if others have had more luck with this app, and partly to document that this might be another app that just doesn't work on GOS.