NGF IGN78 - EPSG:5721

WKT

VERTCS["NGF_IGN78", 
	VDATUM["Nivellement_General_de_la_France_IGN78"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["NGF_IGN78", 
	VDATUM["Nivellement_General_de_la_France_IGN78"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5721"]]

Data from @esri/proj-codes

{
  "wkid": 5721,
  "latestWkid": 5721,
  "macro": "PE_VCS_NGF_IGN78",
  "name": "NGF_IGN78",
  "wkt": "VERTCS[\"NGF_IGN78\",VDATUM[\"Nivellement_General_de_la_France_IGN78\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"NGF_IGN78\",VDATUM[\"Nivellement_General_de_la_France_IGN78\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5721\"]]",
  "description": "NGF IGN78",
  "authority": "EPSG",
  "version": "6.6(9.3.0.0)",
  "deprecated": "no",
  "areaname": "France - Corsica onshore",
  "extent": {
    "slat": 41.31,
    "nlat": 43.07,
    "llon": 8.5,
    "rlon": 9.63
  }
}