Export von Gantt- Dateien für MS Project 21

Hello, I want to export an Gantt- Projekt, that other Project- Partners can import the file in Microsoft Project 21. I use Gantt 2.8.11 and tried it by using the option export, but both Possibilitys in the ‘export-Assistant’ did not work. how can I become a better result.
Thank you.

GanttProject 2.8.11 was released 4 years ago. Did you try using GanttProject 3.3?