"Convert / Save" a "slice" from a FLAC file : the resulting file as no metadata for duration

I want to extract a slice from an existing flac file : e.g. from 00:00:00 to ̀00:09:33. I use the "Convert / Save" entry from the "File" menu. Everything works superbly exept that the resulting file has no metadata for its duration. This is consistant on a dozen of such extractions.

The following thread seems relevant : https://stackoverflow.com/questions/60653531/ffmpeg-flac-audio-file-duration-in-metadata-is-0

Using the proposed command line ffmpeg -i input.flac -c:v copy -c:a flac output.flac I was able to correct one file, I did not try others.