Get the outer geometry of a filtered a feature collection GEE

Question

I am filtering a feature collection using some adapted code from other scripts I have, is it a way to obtain only the outer geometry and not the union of all features? Simplify don't do that.

var region = ee.Geometry.Polygon(
        [[[-168.4122049619641, 71.96304726349818],
          [-168.4122049619641, 37.15429194943178],
          [-43.78329871196412, 37.15429194943178],
          [-43.78329871196412, 71.96304726349818]]], null, false);


var congo = ee.Feature(
  region
);


// Load a FeatureCollection from a table dataset: 'RESOLVE' ecoregions.
var ecoregions = ee.FeatureCollection('RESOLVE/ECOREGIONS/2017');

//Map.addLayer(ecoregions, {}, 'default display');

// Subset protected areas to the bounds of the ecoregion feature
// and other criteria. Clip to the intersection with congo.
var protectedAreas = ecoregions
  .filter(ee.Filter.and(
    ee.Filter.bounds(region),
    ee.Filter.eq('BIOME_NUM', 6) // 4. Temperate broadleaf and mixed forests
  ))
  .map(function(feat){
    return congo.intersection(feat);
  });

Map.addLayer(protectedAreas, {}, 'NA Boreal Forest');  

Answer 1

I believe dissolve() does the trick:

protectedAreas.geometry().dissolve()

https://code.earthengine.google.com/78288afe956f3c0efb8df57f90d8059f