If you tried hard, you could see bits and pieces of 3.1 interface in 95, but it was because you were running a fpga tool with an ancient file dialog, or you went out of your way to run progman, or an old installer launched progman for some reason (I think that sometimes happened, but could be misremembering 25 years ago). As opposed to newer windows where they change things, but not everything.
I think 95 was the last time Microsoft did user research to figure out how to make UI that is appealing and useful. At least, it was the last time they published anything about it. Newer stuff may be more appealing, but seems to make things require more clicks or wait to load more often, meaning it takes users longer to do tasks, and is less useful.