Grasshopper assembly to read .GeoJSON files, using Newtownsoft.Json
Go to github release page to download.
After downloading the file, make sure to unlock/trust it and then drag-and-drop into a running Grasshopper interface.
If you are having trouble unblocking the file, please refer to this video.
You may find the component installed under the RhinoGIS category in the Grasshopper Interface.
Good luck!