As an intermediate step Onshape is fine, I was surprised it imported correctly, while others app gave errors. You just need the DXF converted to continue on Shapr.
If QCAD is no longer there the next option is not exporting as DXF or DWG but as PDF so you can open and save as DXF in Inkscape.
When you Save As match these settings.
If you find another solution let me know.