What version of QMac are you using? Which specific report are you trying to export? Screenshots would be helpful.
If you are clicking menu File > Export > Register Transactions to CSV File with a report open, that will be grayed out because that's for register transactions, not reports. To export a report (in current QMac), you need to click the Export button in the toolbar at the top of the report.
Are you trying to export the report from the File > Export menu? Or from clicking Export at the top of the report? The latter is what you need.
If that's what you're doing, could you step back and give us a few details about the type of report it is (such as Type=Summary, Row=Category, Column=Time, Interval=None), and perhaps a screenshot of where you're seeing it grayed out.
Thank you both.