the answer is online casinos. the reason for this is they have a lower cost for starting and operating the casino if it is online so there is not much needed to break even or get profit but physical casinos has a lot of costs just from the building, working employees, electricity or other maintenance needed.
I have limited knowledge on this but let me answer the best way that I can. Those who own and operate online casinos and physical casinos already would have done some swot analysis and concluded on which of the business models works best for them based on many factors. Operational cost is not even the main thing. Looking at operational cost, you will likely be surprised that those who operate online casino spend more because of serve more than one countries and spend more on servers and other important tech stuff and they are even more at risk of losing money to hacks. But those who operate physical casinos will be aliens to these problems and will even make more profit. I don't know but that is what I like to think.