droptimal написавI'm curious how mutli skeleton with the "single atlas" option is supposed to work if it generates only 1 file. Is there something I'm not understanding with how that export option is supposed to work?
There isn't usually a need for Skeleton Viewer to load skeleton data and an atlas that contains the images for multiple skeletons. Skeleton Viewer is a simple tool that uses spine-libgdx to load and display a skeleton. It is useful to make sure things are working correctly using spine-libgdx, which is the reference implementation that all the other runtimes are based on. In your actual application you can easily load a single atlas and have all your skeletons use it.
BTW, I'd suggest to enable the Windows setting so you can see file extensions. Things can be very confusing when Windows hides your file extensions.