Hi!

You are combining options that won’t work. If you want to create an iOS malicious app then you can set the architecutre to osx-app nor can select the format as exe, that’s a windows thing only, neither add .exe extension to the name of the file. So I’ll suggest to remove -a anf -f and use a file name without extensions for -o, msfvenom should add the proper values by default.

Greetings!
Diego