Implementation of Mobile Application

Is it possible to make an application to control certain aspects in a game made with Unreal Engine?

For example, player one would play the game using the console, while a second player uses the mobile application to change the outcome of the game itself, or maybe help unlock doors by playing minigames or something.

Thank you in advance for the help.

Yes, you can have things linked across different platforms, just note that something like a console game can have issues with that due to restrictions of the console manufacturer. Though something like a mobile linked app is likely to be fine, it’s mostly if you want to link to a different console.