Well, Unity is a good example of this, because most of their techniques involve transforming your C# code or assembly into something else that doesn't run on th

Well, Unity is a good example of this, because most of their techniques involve transforming your C# code or assembly into something else that doesn't run on the .NET runtime, or else having you structure it so that it can be offloaded - directly into C++ code in IL2CPP, or using LLVM to turn the IL bytecode into machine code with Burst. I don't know much about the Jobs/DOTS stuff but I assume the restrictions around it and how you use it are either due to it being based on a strict call-out to C++ code, or else some underlying "unsafe" C# code that Unity is managing safety around via structure - from a little reading it sounds like probably both.