I have never seen this before, spectacles which come apart in the middle and can be clicked back together again.
Is there a word for this?
One manufacturer (Clic) calls them front-connecting:
Clic goggles is the pioneer in front connecting eyewear.
Apparently they are intended to go over existing glasses, or around helmets and the like, or perhaps where mask loops or hearing aids might interfere with positioning the arms over the ears.
The frames you ask about are sometimes called pull-apart frames, magnetic glasses, front connection frames or front snap connect eyeglasses.
Front connection frames magnetically fasten across the bridge of the nose. When not in use they hang conveniently around your neck. Source: https://www.magneteyesuk.co.uk/
While researching this on the internet I came across an article that tells you absolutely everything a person might ever need to know about spectacles. Fascinating! https://www.bantonframeworks.co.uk/blogs/guides/parts-of-glasses