Well, there are very few people who make a full time living from performance only. Most of those have spouses with reliable employment, health insurance, pension, etc.
As I noted in the other thread, there are a lot of versions of "professional musician". The guy who plays ten gigs a month for money, and drives Uber, mows lawns, and works behind the counter at the auto parts store to be able to survive, is he a professional? The guy who plays the same number of gigs, but has a teaching studio of 25 students, is he a professional? The guy who plays the same number of gigs, but makes his monthly nut selling insurance? How about when the guy who was playing ten gigs a month for money, marries an RN and quits all non-musical employment, does that convert him from "semi professional" to "full professional"?
To me, I think "professional" vs. "amateur" really comes down to the gig, rather than the individual person. When I was playing in society bands, we'd sometimes get $400 a man for a big dinner-dance - nice pay for the late 1990s. Some of us had full time non-musical professional jobs, some of us were high school band directors, some of us played gigs and taught students, some of us played gigs and had various minimum wage jobs, some played gigs and kept the children while the spouse went off to work every day at the hospital or software company. We were all getting paid the same, and we were expected to meet the same standards of quality in our performance. I'd call it a professional gig, being played by a band full of people with varying ways of making their income.