The most likely cause is a shutter problem, especially on an older mechanical camera that has sat unused for years. If the shutter was stuck closed for most of the roll, the film would stay blank because no light reached it. It may have freed up only on the final frame, which would explain why that was the only image recorded.

A less likely possibility is exposure settings that were so far off that frames got effectively no exposure, but if every frame except the last was completely blank, a stuck shutter is the stronger explanation.

Before shooting another roll, open the camera back with no film loaded, point the camera toward a bright light, and fire the shutter at several shutter speeds. You should be able to see the shutter open briefly. If you don’t see light passing through consistently, the camera likely needs service.

Also check that the aperture and shutter speed are set appropriately for the scene, since film needs enough light to record an image at all.