If you have created an Insights report that you would like to export, you can select the download CSV button in the upper right-hand corner of the report. At this time, there is a 100 segment limit on Insights exports, So for extremely high cardinality properties the export may not return all segments, but it will return the top 100.
The ability to download a CSV of your report data depends on which Engagement plan you are currently on. If you are on a Business or Enterprise plan, you will have access to this feature. To see which plan you are on, please check your Billing Plan under Account in your Mixpanel project. For more information on the different Engagement plans, please see our pricing page.