After my long search, the only solution to develop apps for Augmented Reality/Virtual Reality with React Native seems to be ViroReact (https://viromedia.com/viroreact/).
Especially now that Expo has stopped their own AR project, it would be great if Expo would support ViroReact. ViroReact is easy to use and allows the simultaneous development of AR/VR experiences for Android and iOS. Perfect to fill the gap of AR/VR in the Expo ecosystem.
According to some response, the Viro team would be ready for this (https://github.com/viromedia/viro/issues/63#issuecomment-404210736).