To add some notes to this from another IOS user. There are two places within IOS settings that allow you to set the ability for Minecraft to use cellular data and one within the game itself. All three of those have been verified as allowing it. Since the last update to the app, when not connected to a wifi, all online friends disappear, personal realms disappear and public realms diasappear. I have tried this in multiple areas with great cellular signal. I can connect to a wifi and suddenly they all appear. This causes issues not only in areas with no wifi, but in places i frequent that do not allow connection to realm games using their wifi. To be reiterate and be clear that this is a bug, all three available settings are marked to allow cellular data and the game itself does not.
Image 99002054 is with wifi on, image 44C8A775 is directly after turning off wifi, and image 73ac5bac is the realms tab when on LTE