GLB is a type of 3d object file format, so yes, it would be a 3d image that could be rotated around and stuff. If you've got an up-to-date version of Windows 10 on your computer, you'll be able to save and open GLB files in Paint 3D. When saving a 3d image in Paint 3D, GLB is the first option listed when exporting the objects you make in it.
I've added that file format, as well as FBX and 3MF, as allowed file types to be attached to posts, since Paint 3D is standard in Windows 10!