Factoring in marketing costs and the theaters taking their cut of the profits, Megalopolis would need to make at least $300 million to break even. I think it's safe to say that's not happening.
It would have been THE worst opening for a $100 million movie ever, had it not been for Pluto Nash's horriffic opening 22 years ago.
Even adjusting for inflation, Pluto Nash still wins. It opened to $3.5M in today's money.
I feel like there hasn't been much marketing for Megalopolis. Could be a factor. I'd say the long run time doesn't help, but Oppenheimer counters that point.