As for specific technologies, here's my rough list of what we're either starting to forget, had to re-remember recently, or have completely forgotten:
- low latency, simple, native UIs that don't require a designer
- operating on data locally first, and not over a network
- information highway instead of doom-scrolling
- message passing (constantly re-discovered, and then forgotten because people complain it's not RPC)
- relational and logic programming - I firmly believe this will come back one day, but it will be called something else and look new.
- static memory allocation. turns out it's still incredibly fast to do this.
- software design