I am trying to display a TopoJSON file i took here : https://www.data.gouv.fr/en/datasets/contours-des-communes-de-france-simplifie-avec-regions-et-departement-doutre-mer-rapproches/#resources

In Leaflet, and I am having some troubles.

I followed this tutorial : http://bl.ocks.org/hpfast/2fb8de57c356d8c45ce511189eec5d6a

And tried different things, but got nothing.

I tried : displaying the data in qgis (it works)
converting the file to EPSG:3857
saving to GeoJSON.

I stay in front of a blank map.

Edit: added relevant code

Here is the code i use :
As advertised, the exact same as the tutorial i mentioned
            
        var map = L.map('map').setView([42.098115, 9.131013], 7);

        var osm = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
            maxZoom: 19,
            attribution: '&copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a>'
        }).addTo(map);

        var json_data;

        //extend Leaflet to create a GeoJSON layer from a TopoJSON file
        L.TopoJSON = L.GeoJSON.extend({
            addData: function (data) {
            var geojson, key;
            if (data.type === "Topology") {
                json_data = data;
                console.log(data.type);
                for (key in data.objects) {
                    console.log(key);
                    console.log(data.objects.hasOwnProperty(key));
                    if (data.objects.hasOwnProperty(key)) {
                        console.log(data.objects[key]);
                        geojson = topojson.feature(data, data.objects[key]);
                        L.GeoJSON.prototype.addData.call(this, geojson);
                    }
                }
                return this;
            }
            L.GeoJSON.prototype.addData.call(this, data);
            return this;
            }
        });

        L.topoJson = function(json, options) {
            return new L.TopoJSON(json, options);
        };

        //create an empty geojson layer
        //with a style and a popup on click
        var geojson = L.topoJson(null, {
            style: function(feature){
            return {
                color: "#000",
                opacity: 1,
                weight: 1,
                fillColor: '#35495d',
                fillOpacity: 0.8
            }
            },
            onEachFeature: function(feature, layer) {
            layer.bindPopup('<p>'+feature.properties.name+'</p>')
            }
        }).addTo(map);
        //fill: #317581;
        //define a function to get and parse geojson from URL
        async function getGeoData(url) {
            let response = await fetch(url);
            let data = await response.json();
            console.log(data)
            return data;
        }
        
        //fetch the geojson and add it to our geojson layer
        getGeoData('communes_corse_espg.topojson').then(data => geojson.addData(data));


the topojson file is local, but i see in the console and my various console.log that it was correctly loaded

Edit:

When i carefuly inspect my json, i see that the coordinates calculated by the topojs library are absolutely insane, like for instance 846981.4360214358, 6564107.359928558
While the ones from the demo are closer to 6.887404954866349, 53.29824733215662