Massively massively more distracting to me than coughs or whatever, the glint just catches my eye and attention away from the screen, even rows in front and is so much more off putting to me that an occasional cough or whatever. Totally immersion breaking.
Remember there used to be a lot of hand wringing about the younger generation always being on their phones in cinemas but, in my experience it’s middle aged people who can’t possibly go two hours without looking at notifications. Boils my piss.