Reykjavik 1900 - EPSG:4657

WKT

GEOGCS["GCS_Reykjavik_1900", 
	DATUM["D_Reykjavik_1900", 
		SPHEROID["Danish_1876", 6377019.27, 300.0]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GCS_Reykjavik_1900", 
	DATUM["D_Reykjavik_1900", 
		ELLIPSOID["Danish_1876", 6377019.27, 300.0]], 
	PRIMEM["Greenwich", 0.0], 
	CS[ellipsoidal, 2], 
	AXIS["Latitude (lat)", north, 
		ORDER[1]], 
	AXIS["Longitude (lon)", east, 
		ORDER[2]], 
	ANGLEUNIT["Degree", 0.0174532925199433], 
	ID["EPSG", "4657"]]

Data from @esri/proj-codes

{
  "wkid": 4657,
  "latestWkid": 4657,
  "macro": "PE_GCS_REYKJAVIK_1900",
  "name": "GCS_Reykjavik_1900",
  "wkt": "GEOGCS[\"GCS_Reykjavik_1900\",DATUM[\"D_Reykjavik_1900\",SPHEROID[\"Danish_1876\",6377019.27,300.0]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GCS_Reykjavik_1900\",DATUM[\"D_Reykjavik_1900\",ELLIPSOID[\"Danish_1876\",6377019.27,300.0]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433],ID[\"EPSG\",\"4657\"]]",
  "description": "Reykjavik 1900",
  "authority": "EPSG",
  "version": "6.5(9.0.0)",
  "deprecated": "no",
  "areaname": "Iceland - mainland",
  "extent": {
    "slat": 63.34,
    "nlat": 66.59,
    "llon": -24.66,
    "rlon": -13.38
  }
}