RT 1990 - EPSG:4124

WKT

GEOGCS["GCS_RT_1990", 
	DATUM["D_RT_1990", 
		SPHEROID["Bessel_1841", 6377397.155, 299.1528128]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GCS_RT_1990", 
	DATUM["D_RT_1990", 
		ELLIPSOID["Bessel_1841", 6377397.155, 299.1528128]], 
	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", "4124"]]

Data from @esri/proj-codes

{
  "wkid": 4124,
  "latestWkid": 4124,
  "macro": "PE_GCS_RT90",
  "name": "GCS_RT_1990",
  "wkt": "GEOGCS[\"GCS_RT_1990\",DATUM[\"D_RT_1990\",SPHEROID[\"Bessel_1841\",6377397.155,299.1528128]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GCS_RT_1990\",DATUM[\"D_RT_1990\",ELLIPSOID[\"Bessel_1841\",6377397.155,299.1528128]],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\",\"4124\"]]",
  "description": "RT 1990",
  "authority": "EPSG",
  "version": "6.5(8.0.1)",
  "deprecated": "no",
  "areaname": "Sweden",
  "extent": {
    "slat": 54.96,
    "nlat": 69.07,
    "llon": 10.03,
    "rlon": 24.17
  }
}