Hello Sanjay,
The limits to export from the visual itself are, for CSV the limit is 1m rows or 500MB.
For Excel, the limit depends on the number of fields you have selected on your dataset. The maximum is 100k rows but when you start adding more columns the number of rows exported decreases. For more info - see Exporting data from visuals - Amazon QuickSight
Most likely the same limitation applies to Q as well.
Some similar context here - I am trying to export a table to Excel, but is only exporting 10,000 lines with 2.9 MB - #2 by andres007
Hope this helps.
Cheers,
Deep