Turn one model or a whole folder of STEP, STL and OBJ files into spinning GIF, WebP or AVIF previews, from the interface, Watch Folders or the command line, without a 3D program.
Short answer: reaConverter renders a 3D model at a series of angles and saves the frames as one animated file. Open Menu → Loading settings → 3D formats, tick Create multiple frames, set 36 frames and Change Y from 0 to 360. Then save as GIF with an Animation delay time of 5. It works on one model or a whole folder, offline.