It began starting in 1970 through to the 1980s.
Then in the 1990s is when it flipped.
https://www.economicshelp.org/blog/221939/economics/the-two-speed-us-economy-2026/
You can clearly see in 1970 things were in the much more balanced productive state, and we are in an upside down economy. This will not last much longer with AI.
I often say that the 70's were pea. People like to point out all sorts of things that got better from then but its really about we were generally looking to progress then for the last few decades and that kinda stopped. It was a slow decline though so we made some progress but it went from like generally steps forward to 2 steps forward one back to one forward one back and then 1 forward and 2 back and now we are just generally moving backward.