Go to Dashboard > Custom Blocks, create a new custom block and name it “Mobile Menu” (or any other name you like).
Please edit the custom block with Elementor. You can add any elements/widgets inside.
Then, please open the Customizer > Site Header > Fullscreen/Mobile Menu, then select the “Mobile Menu” custom block you’ve created. (Click the screenshot below to see the larger one.)
You can change more options, such as Entrance Animation, Width, etc.