Are 90° ‘spy’ right-angle mirror lens attachments real, and what are they called?

Yes. These are real, but they’re usually not true lenses by themselves. They’re typically a right-angle mirror attachment that screws onto the front filter threads of an existing lens, sometimes sold as a right-angle mirror lens hood, angle mirror lens, or “spy lens.”

They work by using a mirror inside a tube to bend the view about 90°, so the camera can appear to point one way while photographing to the side. Some versions may have a simple front glass element, but the key part is the mirror, not complex lens optics.

These accessories have been sold by various brands and in different thread sizes, so compatibility depends on your lens’s filter diameter. In practice, they’re novelty/specialty accessories rather than common everyday tools.