This seems likely to be controversial but I want to put forward "sales". Every so often I wonder if I should spend several months in a job like selling cars, where things are presumably really stark, but so far I've generally ended up doing something more kosher and traditionally "geeky" like data science.
However, before I knew a marketable programming language I had a two separate "terrible college jobs" that polished a lot of stuff pretty fast: (1) signature gathering for ballot measures and (2) door to door campaigning for an environmental group.
Signature gathering was way way better than door-to-door, both financially and educationally. Part of that is probably simply because there were hundreds of opportunities per hour at peak periods, but part of that might have been that I was hired by a guy who traveled around doing it full time, and so he had spent longer slower cycles leveling up on training people to train people to gather signatures :-P
Every so often I wonder if I should spend several months in a job like selling cars
I did just this. It was rather difficult, but my confidence and communication skills did improve quite a bit.
A lot of my significant personal improvement happened as a result of highly measurable progress and tight feedback loops. For example: