iOS 64-bit support is implemented with the scripting backend called IL2CPP. It runs with your C# code.
El IL2CPP runtime combina un compilador ahead of time (AOT) con una maquina virtual para convertir assemblies a C++ mientras aprovecha los compiladores estándar C++ de plataforma para producir binarios nativos. El resultado neto es un rendimiento significativamente mayor, la compatibilidad de la plataforma y la facilidad de mantenimiento.
IL2CPP is the only scripting backend to support deploying to ARM 64-bit on iOS, and is thus mandatory to deploy to the Apple App Sstore for releasing new apps.
To read more about IL2CPP, see the blog posts The future of scripting in Unity and Apple iOS 64-bit support in Unity.
Select IL2CPP in the Scripting Backend drop-down menu on the Player window.
By default it will build for Universal architecture (including both ARM64 and ARMv7); if needed you can switch to specific architecture on the Player window. There are a number of things that should be done before your application is up and running in 64-bits:
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