Mods are currently only available on PC/Mac/Android. If you use iOS, too bad. This needs to change.
I’ve heard that mods and custom maps cannot be used on the iOS version because of issues with the OS and security concerns. I suggest that to be able to use modded maps on iOS, the game can add a custom map feature in-game, just like how we can build planes. This way, downloading a map can just create a new save file instead of changing a game like a mod.
Of course, maps are still just like other mods; they just change a different aspect of the game. It may, then, be hard to make maps separate from mods but it may still be possible so I am suggesting it.

EDIT: Android had mods removed too :(
I guess mobile sucks for gaming either way