IGN 1989 - EPSG:5758

WKT

VERTCS["IGN_1989", 
	VDATUM["IGN_1989"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["IGN_1989", 
	VDATUM["IGN_1989"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5758"]]

Data from @esri/proj-codes

{
  "wkid": 5758,
  "latestWkid": 5758,
  "macro": "PE_VCS_IGN_1989",
  "name": "IGN_1989",
  "wkt": "VERTCS[\"IGN_1989\",VDATUM[\"IGN_1989\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"IGN_1989\",VDATUM[\"IGN_1989\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5758\"]]",
  "description": "IGN 1989",
  "authority": "EPSG",
  "version": "6.6(9.3.0.0)",
  "deprecated": "no",
  "areaname": "Reunion - onshore",
  "extent": {
    "slat": -21.42,
    "nlat": -20.81,
    "llon": 55.16,
    "rlon": 55.91
  }
}