Natural Earth II (sphere) - ESRI:53078

WKT

PROJCS["Sphere_Natural_Earth_II", 
	GEOGCS["GCS_Sphere_GRS_1980_Mean_Radius", 
		DATUM["D_Sphere_GRS_1980_Mean_Radius", 
			SPHEROID["Sphere_GRS_1980_Mean_Radius", 6371008.7714, 0.0]], 
		PRIMEM["Greenwich", 0.0], 
		UNIT["Degree", 0.0174532925199433]], 
	PROJECTION["Natural_Earth_II"], 
	PARAMETER["False_Easting", 0.0], 
	PARAMETER["False_Northing", 0.0], 
	PARAMETER["Central_Meridian", 0.0], 
	UNIT["Meter", 1.0]]

WKT2

PROJCRS["Sphere_Natural_Earth_II", 
	BASEGEOGCRS["GCS_Sphere_GRS_1980_Mean_Radius", 
		DATUM["D_Sphere_GRS_1980_Mean_Radius", 
			ELLIPSOID["Sphere_GRS_1980_Mean_Radius", 6371008.7714, 0.0]], 
		PRIMEM["Greenwich", 0.0], 
		CS[ellipsoidal, 2], 
		AXIS["Longitude (lon)", east, 
			ORDER[1]], 
		AXIS["Latitude (lat)", north, 
			ORDER[2]], 
		ANGLEUNIT["Degree", 0.0174532925199433]], 
	CONVERSION["Natural_Earth_II", 
		METHOD["Natural_Earth_II"], 
		PARAMETER["False_Easting", 0.0], 
		PARAMETER["False_Northing", 0.0], 
		PARAMETER["Central_Meridian", 0.0]], 
	CS[Cartesian, 2], 
	AXIS["Easting (X)", east, 
		ORDER[1]], 
	AXIS["Northing (Y)", north, 
		ORDER[2]], 
	LENGTHUNIT["Meter", 1.0], 
	ID["Esri", "53078"]]

Data from @esri/proj-codes

{
  "wkid": 53078,
  "latestWkid": 53078,
  "gcsWkid": 104047,
  "macro": "PE_PCS_SPHERE_NATURAL_EARTH_II",
  "name": "Sphere_Natural_Earth_II",
  "wkt": "PROJCS[\"Sphere_Natural_Earth_II\",GEOGCS[\"GCS_Sphere_GRS_1980_Mean_Radius\",DATUM[\"D_Sphere_GRS_1980_Mean_Radius\",SPHEROID[\"Sphere_GRS_1980_Mean_Radius\",6371008.7714,0.0]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Natural_Earth_II\"],PARAMETER[\"False_Easting\",0.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",0.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "PROJCRS[\"Sphere_Natural_Earth_II\",BASEGEOGCRS[\"GCS_Sphere_GRS_1980_Mean_Radius\",DATUM[\"D_Sphere_GRS_1980_Mean_Radius\",ELLIPSOID[\"Sphere_GRS_1980_Mean_Radius\",6371008.7714,0.0]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Longitude (lon)\",east,ORDER[1]],AXIS[\"Latitude (lat)\",north,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433]],CONVERSION[\"Natural_Earth_II\",METHOD[\"Natural_Earth_II\"],PARAMETER[\"False_Easting\",0.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",0.0]],CS[Cartesian,2],AXIS[\"Easting (X)\",east,ORDER[1]],AXIS[\"Northing (Y)\",north,ORDER[2]],LENGTHUNIT[\"Meter\",1.0],ID[\"Esri\",\"53078\"]]",
  "description": "Natural Earth II (sphere)",
  "authority": "Esri",
  "version": "10.4.0",
  "deprecated": "no",
  "areaname": "World",
  "extent": {
    "slat": -90,
    "nlat": 90,
    "llon": -180,
    "rlon": 180
  }
}