Layers

Layer > Add Layer > Add ArcGIS REST Server Layer > New
Name: Layers
URL: https://www.mapping.cityoflondon.gov.uk/arcgis/rest/services/COMPASS_Public_Health/MapServer

Insert > Connections > Server > New ArcGIS Server
Server URL: https://www.mapping.cityoflondon.gov.uk/arcgis/rest/services/COMPASS_Public_Health/MapServer

fetch('https://www.mapping.cityoflondon.gov.uk/arcgis/rest/services/COMPASS_Public_Health/MapServer/0/query?where=1%3D1&outFields=*&f=geojson')
  .then((r) => r.json())
  .then((geojson) => L.geoJSON(geojson).addTo(map));

import geopandas as gpd
gdf = gpd.read_file(
    'https://www.mapping.cityoflondon.gov.uk/arcgis/rest/services/COMPASS_Public_Health/MapServer/0/query?where=1%3D1&outFields=*&f=geojson'
)