We're already only a few months away from 2022, most (if not all) carmakers present on the EU market have included back-up cameras in their vehicles. I know that my brother's Dacia Logan built in 2019 already had one.
Backup cameras have been an optional extra for a long time sure, but I don't think I'm aware of any car that actually comes standard with one. Well, maybe a Mercedes-Benz S-Class. I do have a backup camera in my 10-year-old Benz, but I imagine that the original owner paid a four-digit amount of euros for it back in the day.
'Rear Visibility' is required in new cars in US by FMVSS 111.
Test procedure mandates field of view to rear of vehicles during backing, that are practical to satisfy with cameras. mirrors would require like a periscope to satisfy.