North Rona - EPSG:5745

WKT

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

WKT2

VERTCRS["North_Rona", 
	VDATUM["North_Rona"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5745"]]

Data from @esri/proj-codes

{
  "wkid": 5745,
  "latestWkid": 5745,
  "macro": "PE_VCS_NORTH_RONA",
  "name": "North_Rona",
  "wkt": "VERTCS[\"North_Rona\",VDATUM[\"North_Rona\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"North_Rona\",VDATUM[\"North_Rona\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5745\"]]",
  "description": "North Rona",
  "authority": "EPSG",
  "version": "6.15(9.3.0.0)",
  "deprecated": "no",
  "areaname": "UK - North Rona onshore",
  "extent": {
    "slat": 59.07,
    "nlat": 59.19,
    "llon": -5.92,
    "rlon": -5.73
  }
}