If you are exporting after filtering orders in Shopify, the maximum number you can export is 50 orders at a time. This limitation is from Shopify's built-in filters; they do not currently allow more than 50 orders to be sent to any app (not just Exportify) from the filter interface.
Should you want to export more than 50 orders at the same time, you can definitely do so by choosing from several of our pre-set date range options, or create a custom date range of your choice with options for various order, financial, and fulfillment status in the Exportify dashboard.
For more details on how you can export your orders, please check this help article out: How do I export my orders?