>However I know that graphene are (were?) Working on a store of their own at some point, so when that is released my opinion may change.

They have their own store now, https://github.com/GrapheneOS/Apps/releases.

Currently, it lists only graphene apps like Secure Camera, graphene PDF vewier, Auditor, Sandboxed Play services. Also, it only works for Android 12 and above, not only on GrapahenOS but other OS like Calyx, Lineage and it forks etc.

They are planning to add other graphene apps too, like Vandaium* etc. Non-graphene apps (like apps available on f-droid), I don't think they will be added. This store seems to be only for Graphene Apps.