FWIW given the following HTML:

<select>
  <option></option>
</select>

does result in an empty option (tested in Chrome and Firefox):

I think untitled/labelled layers should be presented, because you can hide layers you don't want shown by adding the hidden attribute. I do think they could have a generated "Map Layer" or some such, so that screen readers would say them. TBD how well this layer control works for screen readers.

Currently, when GeoJSON layers (with no label) are pasted to the mapml-viewer, they get a default localized name of "Layer". I wonder if the same semantics should be used for untitled/unlabeled layers.

For ex. Pasting the following geojson to a mapml-viewer results in a new layer with the "Layer" label:
{ "type": "FeatureCollection", "features": [ { "type": "Feature", "properties": {}, "geometry": { "coordinates": [ [ -75.70390559334825, 45.4080260348249 ], [ -75.68642173896234, 45.428944769710455 ] ], "type": "LineString" } } ] }

To test this bug, add the following layer to the sandbox:

<layer- checked>
        <map-meta name="projection" content="OSMTILE"></map-meta><map-feature zoom="10">
        <map-featurecaption>Copied OSMTILE gcrs location</map-featurecaption>
        <map-properties>
            <h2>Copied OSMTILE gcrs location</h2>
            <div style="text-align:center">-75.866089 45.463020</div>
        </map-properties>
        <map-geometry cs="gcrs">
          <map-point>
            <map-coordinates>-75.866089 45.463020</map-coordinates>
          </map-point>
        </map-geometry>
      </map-feature>
</layer->

The layer shows up as undefined, it should instead be called Layer