Anything that costs $0 to make a copy of, but is sold at premium. Enterprise software like Oracle, etc. Digital Music. Streamed Movies and shows (Netflix).
Also, anything that costs nearly $0 at scale, but is sold at premium. Internet service. Cellular service.
There's a staggeringly long list of things that are now post-scarcity because they're digital. Each item used to be a luxury available to few instead of a thing that scales to all.
So here's a new way to ask an old question: What's something that should be post-scarcity, but currently isn't?