> Operating systems of that era were designed based on UX research to help people use the unfamiliar operating system.

I have a lot of thoughts on things like PC usability today. You're right that UX research would have heavily contributed to the design on these older systems. As computers moved from the warehouse to the living room they had to be easier to use and understand for people without CS degrees. I think it is fair to assume *some* things about what people these days are familiar with when it comes to the desktop GUI, but usability should receive more focus now even if it slightly hinders aesthetic. A friend of mine has been teaching a college program for video editing and she has students who needed her to explain what files and folders are. This is not the first time I've heard of things like this.

Smartphones and tablets have obfuscated so many basic functions and features that it is actively harming people's understanding of how to use a computer. Things like window sizing, executables, how apps know where things are, and how programs are installed. Android does allow users to peek behind the curtain more than iOS but Google has been going down the path of locking down Android. I haven't been in an elementary school classroom for like 17 years but I remember having computer lab time where we would learn how to use Windows 95/98. I think what has benefited my friends and others my age (~30) is that we grew up when computers were in the home and were usable enough for us to log in and intuit our way around but there was enough friction that made it so we would have to figure things out on our own.