Hello,
For a few releases now (I'd say two to three months), I have duplicate notifications for a lot of apps (Graphene or not).
For example, if I have a missed call, I see two notifications for the same event (missed call): they both have the same information (person, time...). I'm using the Tasks application, and I have the same issue (duplicate notifications).
I don't have it for services which use their own notification process (such as FairEmail and ntfy), so my take would be an issue in the GrapheneOS notification system.
I don't use Google Play on this profile (but have it enabled on other profiles).
I don't remember changing anything in the configuration linked to the notification...
Thanks in advance for your help!