As far as I know it is not possible to access the search fields, and use these in a microflow. What you could try is to create a search object that has the fields available like in the search box of s standard grid. Then perform the search action based on the data in the search object in a microflow. Link the results of the microflow to the search object and refresh the search object. To display the data create a page for the search object that has a grid with the search result nested in the outer dataview. Now for the export you can reuse the query part of the (sub)microflow you already created to retrieve the list that you want to export and pass the result to the microflow creating the export.
In this way you can search and have the grid still be single selection and pass the list of search results based on the selection in the search fields to the export function. Hope this helps you in finding a solution.