As you may know Gravity Forms doesn’t provide any built-in integration for Elementor. I’m not aware of any third-party solution to achieve your goal out of the box, but if Elementor support can provide you any custom JavaScript action code to trigger the popup, you could append that code to the submit button as in the example in the following GF filter documentation page: https://docs.gravityforms.com/gform_submit_button/#h-4-append-a-javascript-action-to-the-button