Mangione had back issues and apparently some difficulty in getting treatment for it, but he wasn't insured by UHC. According to his manifesto, he chose Brian Thompson as his victim because UHC was the largest health insurance company in the United States.

His alleged* manifesto. There is no reliable evidence that Luigi Mangione committed any crime. It seems more likely that Brian Thompson was killed by a disgruntled customer.

It made no sense that he targeted an underling instead of UNH’s head honcho.