DHHN12 height - EPSG:7699

WKT

VERTCS["DHHN12_(height)", 
	VDATUM["Deutsches_Haupthoehennetz_1912"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["DHHN12_(height)", 
	VDATUM["Deutsches_Haupthoehennetz_1912"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "7699"]]

Data from @esri/proj-codes

{
  "wkid": 7699,
  "latestWkid": 7699,
  "macro": "PE_VCS_DHHN12_HT",
  "name": "DHHN12_(height)",
  "wkt": "VERTCS[\"DHHN12_(height)\",VDATUM[\"Deutsches_Haupthoehennetz_1912\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"DHHN12_(height)\",VDATUM[\"Deutsches_Haupthoehennetz_1912\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"7699\"]]",
  "description": "DHHN12 height",
  "authority": "EPSG",
  "version": "8.8.1(10.5.0)",
  "deprecated": "no",
  "areaname": "Germany - onshore",
  "extent": {
    "slat": 47.27,
    "nlat": 55.09,
    "llon": 5.86,
    "rlon": 15.04
  }
}