By design, Tableau Server needs to know exactly which worksheet you want to export data from. If you have a dashboard with multiple visualizations, the server often cannot default to one automatically.
Simply click once on the specific chart or table you want to export. Once the sheet is highlighted (often indicated by a thin grey border), the Download > Crosstab option should become available.
Ask your Tableau Administrator to check the Workbook Permissions for your specific user or group. 3. Dashboard Objects vs. Toolbar
Even if you have selected a sheet, the option will remain greyed out if your user account lacks the specific "Download" capability for that workbook.
Interestingly, some users experience greyed-out crosstab buttons if they have permission to download summary data but lack permissions for Download Image/PDF . tableau server download crosstab greyed out