Overview got translated to "General Presentation" for your locale.
GeoJSON files can only be added as files in a public account using the Content>New Item workflow. With a regular account you have the option to publish it as a hosted feature layer, then could add it to a map.
With a public account you can add a geoJSON file via URL directly to your map.

You can test that by using this URL from the U.S. Geological Survey:
https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/significant_month.geojson