Geoserver WMTS Service REST url

Here is the link that can help you: https://github.com/PDOK/wmts-kvp-to-restful

To use mapbox vector tiles served by GeoServer, you can do it like this:

// First the layer URL pattern
var layerWMTS = 'http://localhost:8080/geoserver/gwc/service/wmts?layer=public:list_parcels_hobart_4326&tilematrixset=EPSG:900913&Service=WMTS&Request=GetTile&Version=1.0.0&Format=application/x-protobuf;type=mapbox-vector&TileMatrix=EPSG:900913:{z}&TileCol={x}&TileRow={y}'

// Now add the layer
map.addLayer({
  'id': 'geoserver',
  'type': 'fill',
  'source': {
    'type': 'vector',
    'tiles': [
      layerWMTS
    ]
  },
  'layout': {
    'visibility': 'visible'
  },
  'source-layer': 'list_parcels_hobart_4326',
  'paint': {
    'fill-color': 'rgba(244, 131, 66, 0.4)',
    'fill-outline-color': 'rgba(244, 131, 66, 0.9)'
  }
})

This is about as simple as it gets. Note that some of the keywords need to be changed, soch as the layer=public:list_parcels_hobart_4326 section of the layer URL, and the 'source-layer': 'list_parcels_hobart_4326' of the layer parameter object. These can be taken from what you have configured in GeoServer.

And just a note to say that I think that GeoServer's vector tiles are pretty good, but it doesn't seem configurable, so you can't change simplification and such. I have a bit of exploration over here, although it's probably not well documented and a bit messy!