Here's labor force participation for prime age workers[1] (which is similar to the prime age Employment-Population Ratio I posted above). The problem with your graph is that it's including everyone 16 and over - so baby boomer retirement makes an impact, as does the ACA (college students not working a job for benefits because they're covered by their parents, people who are retiring earlier because they don't have to wait for Medicare).
Though it's worth noting that even if, for some reason, you wanted to look at everyone over 16, the participation rate is still well above anywhere it was in the 50's, 60's, and most of the 70's. If you're looking at prime age, we're only a couple of percents below the highs in the 90's (and much higher than other periods).
> but I have yet to read any compelling predictions of new job sectors that will employ large numbers of people and can't be automated.
I'm always confused by this argument. Practically every day on HN there are articles about problems that it would be great if more people were working on. Replication crisis? Aging infrastructure? Global warming? Cancer research? Environmental destruction? Food scarcity? Documentation and bug hunting in software? Taking care of frameworks? Early childhood education? Heck, even beyond all the problems on Earth, there are plenty of people who want to work on things like sending people to Mars.
I just can't fathom how people can look at the world and say, "Yep, we don't really need to do anything more than what we're already doing."