I suppose this is not a Microsft product but a Unity product.
IL2CPP (Intermediate Language To C++) is a Unity-developed scripting backend. The IL2CPP backend converts MSIL (Microsoft Intermediate Language) code (for example, C# code in scripts) into C++ code, then uses the C++ code to create a native binary file (for example, .exe, .apk, or .xap) for your chosen platform.
So it would be best if you contact Unity to understand the legal terms in using them.
Hope this resolves your Query!!
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