Can't find an option to turn off cellular data for an application on iPhone (iOS 14)
I can't stand this iPhone &quot;feature&quot;, but for an app to appear in the list where you can turn cellular data on or off:

the app must be launched once with cellular data on;
sometimes it is not enough - you must not only launch the app, you must do something with it actively.

Though, it may be that for newer iPhones this is not longer the case.