I know there's other ways of having 2FA on your mobile device, but whenever people search for the SWTOR security key app without knowing of other ways, they might end up in a bit of pickle.
All you could do is just make it so it works on the newer versions of Android or something. It's definitely not something that would be the highest priority since you can get other ways of doing 2FA for this game, but it would cause a lot less pain when people try and figure it out and try and use the official app when that can no longer be downloaded on newer versions of Android. I am unsure of the iOS version since I do not use apple devices.
But currently on Android version 13, it is unable to be downloaded via official routes.