@Julien_Curro The singleton example you posted should work for this purpose. The realmConfig you are using here is spreadable onto <RealmProvider {...realmConfig} closeOnUnmount={false}>. If you open a Realm with the same config, you get a shared instance of the same Realm.
The only change I would suggest is to change new Realm to Realm.open. Realm.open is async and more suited for a Realm configured with sync settings.
At the moment we do not have a discord, but you are not the first to ask about this. We are currently trying to merge Realm even closer the MongoDB, so hopefully in the near future the discord is more knowledgable on these topics.