You have to create a microflow in which you give or retrieve the complete list, then export this list to excel with an activity in your microflow. You can then download this file with a Download file activity.
You can create an excel export by generating a document with the document generator of Mendix or by using the excel export module of the Mendix Marketplace.
The reason you probably don't export all rows now is because you only pass a limited list as a parameter. The standard excel export button only exports what is visible in the list, so you can also do a specific export based on a filter on your data grid.
The same list will be passed as a parameter in your button, so the microflow you create should not use the parameter but a retrieve from database and then export that.
I have the following configuration
What is the Problem. At first sight, the generated excel file is a match.
You may need to increase the amount of allowed lines on the export to excel button. By default it is quite limited.