If you would like to export multiple bodies as a single STL mesh file, you can do so by creating a single component which contains all the bodies you wish to include.
To do this, first create a new component by clicking “New Component” under the “Create” tool in the toolbar. This opens a panel on the right side of the screen, which prompts you to select one or multiple bodies from the design. Make sure the option “From Bodies” is toggled, select only one body, and then select “Ok”.
After the new component is created, it will appear at the bottom of the browser tree to the right. To add each additional body to this component, simply find the bodies in the tree, and drag them onto the new component branch in the tree.
You can then right-click this component and select “Save As STL” from the drop-down menu to open the “Save As STL” panel. In the panel, you will now see a “Structure” option to create one file for the entire component, or create a separate file for each body. Make sure that “One File” is selected, and you should be good to go from there.