Hi Alexander,
Here are some Conversion that succeeded but in QGIS is not same.
Gpx → Osm
https://app.screencast.com/9BYewaRMFc1SG
Gpx → Gml
https://app.screencast.com/1RsdoDrcUmN3f
Gpx → Gpx
https://app.screencast…...4524 -GPX conversions to Osm/Gml/Gpx/Topojson have some problems...as restriction to Topojson conversion. We can try to delete this...