I have recalculated PTV_Mercator (PTV Spherical Mercator EPSG:505456) coordinates to WGS84 EPGS:4326 coordinates in Excel. And when checking them on Google Maps they show up correct.
But after loading the CSV and trying to combine them with a map (tried several like OSM, QGIS, etc.), I can in no way get them to "overlap". I've read (and tried) the QGIS "Projection"-topic in the manual several times, but I can not get it to work correct.
As requested, I have added a picture of the problem: