Unity uses their own AOT compiler IL2CPP that translates C# code to C++. Mono is an option in builds, but most projects are using IL2CPP nowadays and have been moving to .Net core. Although C++ is king, C# has quickly caught up to be a close 2nd. Unity is used to make 50% of all mobile, pc, and consoles games (according to Unity https://unity.com/our-company).