Okay so like, what if I own the only mall in a large area. Like a rural suburb where there is often only one shopping space/public commercial space. Is there an upper limit where your private property is considered public utility?
Maybe.
I don't think it's a problem if companies with extreme amounts of power have to give up some freedom of banning.
On a sliding scale though, you don't literally become a utility one day.
(And when it comes to "only commercial storefront space in a large area", I expect that to be very rare.)
This is actually very common in rural parts of the us fwiw. There places where the only grocery store is Walmart, and the only other place to shop is dollar general.
In this case there is likely a limit to what a private business can grow into before it wades into the territory of public utility. A tenuous but related situation can be seen in trademarks where Kleenex has actually run entire ad campaigns to make people call generic tissue "tissues".
There's a larger philosophical argument here. Theoretically speaking there should be no limits to private corporations. However, when your corporation becomes a stable of modern life and the conduit of major utilities of society all of the sudden things start to turn into shades of grey.
And this already happens all the time.