Finally got a reply from Marvelous Designer after having sent them a video showing the issue. They say there was a problem with the video tutorial they posted. They have posted a news one and the remeshing to retopology (selected) feature needs some more steps but now it works.The process is not exactly the same as the previous one...

Anyway the new video is available at the Marvelous Designer website in the online manua:

https://marvelousdesigner.zendesk.com/hc/en-us/articles/900000566346-Remeshing-to-Retopology-Selected-ver-5-2-0-