I hope, Cura will support all 3mf format soon.
I have found a workaround!
Earlier, I used this site to fix stl to stl format:
But now, this site redirected to
and I can download fixed model in 3mf format only. Unfortunatelly Cura 2.x.x does not support this 3mf file.
But I have found this site:
what is fix model from stl to stl, so I can load it in cura again.
I hope, this site will work for long time!