1. Mechanical hard drives. These have become a bit more niche, but if you deal with larger files like that movie library the author ought to rip from those fragile optical disks he still has lying around, spinning rust is the far more cost-effective option for storing files you don't use all the time.
2. Phone numbers. His original prediction is that people wouldn't use them, not that people wouldn't remember them and dial them manually. A number of popular messenger services including Signal use phone numbers as identifiers, and I wish they didn't.
3. The fax machine. This absolutely, 100% deserved to be dead a decade ago. Perhaps most faxes aren't actually sent using physical machines anymore, but a lot of businesses and some government institutions treat fax as more secure than purely digital file transfers. My vote in the 2020 US election involved a fax. I'm disappointed in the tech community for not producing a solution that achieved near-universal buy-in from more conservative institutions in the past two decades.
4. Optical disks. I haven't used one in years, and I suspect a lot of other people here are in the same position. There's not that much content I want to watch more than once, so the issue of streaming non-ownership isn't a big problem for me. The author has kids, and kids definitely do that, but there are both legal and less legal ways to obtain permanent copies of content by purely digital means. Note to content sellers: I'm happy to pay for content; don't make it so difficult for me to do so that I seek alternatives.