GS-IRF - EPSG:10256

WKT

GEOGCS["GS-IRF", 
	DATUM["Generalstabens_System_Intermediate_Datum", 
		SPHEROID["Danish_1876", 6377019.27, 300.0]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GS-IRF", 
	DATUM["Generalstabens_System_Intermediate_Datum", 
		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", "10256"]]

Data from @esri/proj-codes

{
  "wkid": 10256,
  "latestWkid": 10256,
  "macro": "PE_GCS_GS_IRF",
  "name": "GS-IRF",
  "wkt": "GEOGCS[\"GS-IRF\",DATUM[\"Generalstabens_System_Intermediate_Datum\",SPHEROID[\"Danish_1876\",6377019.27,300.0]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GS-IRF\",DATUM[\"Generalstabens_System_Intermediate_Datum\",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\",\"10256\"]]",
  "description": "GS-IRF",
  "authority": "EPSG",
  "version": "10.088(13.2.0)",
  "deprecated": "no",
  "areaname": "Denmark - onshore Jutland, Funen, Zealand and Lolland",
  "extent": {
    "slat": 54.51,
    "nlat": 57.8,
    "llon": 8,
    "rlon": 12.87
  }
}