Hi Alexander,
Kmz ->Topojson
Results does not see in QGIS, conversion succeeded.
Link to screencast:
https://app.screencast.com/etcR3d4wLzH7k
Attached samples: input/output/QGIS.
Bug 4571 KMZ to TopoJson -results d…...format does not support 3D geometry, but input Kmz have LineStringZ...format does not support 3D geometry and we will not support too...