Hi Alexander,
I moved to new version 26.5 and here my results:
Please see:
Test data(input/output/QGIS)
5387 Gml Gpx.zip (97.9 KB)
Thanks,...geometries are read correctly KeepZ = true, KeepM = false }); // 2. Re‑project...GpxWriterOptions { // Choose the type of GPX entities you need. //...