While RFC 7946 dropped support in GeoJSON for arbitrary CRS designation, the original 2008 standard supported it. It's a lovely interoperability problem that so

While RFC 7946 dropped support in GeoJSON for arbitrary CRS designation, the original 2008 standard supported it. It's a lovely interoperability problem that sometimes some applications will still produce GeoJSON in a CRS that isn't WGS84 and you get to shuffle it between tools until you get RFC 7946 compliant GeoJSON. There's obviously a small irony that in dropping CRS support to improve interoperability they added interoperability issues between "versions" of GeoJSON and what year an implementation was built and whether or not it support GeoJSON 2008 CRSes (and how it supports them because GeoJSON 2008 "kindly" let you specify the CRS at the FeatureCollection level, the Feature level, and the Geometry level and who knows what it meant when all three disagreed for the same Feature, so RFC 7946 was right to drop it because it was definitely a mess).