Hey, thanks for looking into this. I would like to challenge the assessment though. Adding an attribute to the constructor of that same attribute is something supported in c# and the compiler generates IL that is fully supported by ILSpy and JustDecompile, implying that the IL is valid. I've put up a simple .NET 6 project that reproduces this, but it is something that is supported at least since netstandard 2.0, possible even earlier: https://gist.github.com/nirinchev/b9c614e39bbfe957e7954b6d1093ed10.

Additionally, this appears to be a regression in the IL2CPP compiler - I tested this with Unity 2020.3.10f1 and the project compiles successfully with no code changes. I haven't tried to track down the exact Unity version that introduces the regression since I'm sure you're better equipped to figure it out. Since the UsedImplicitlyAttribute is added to Realm via the Remotion.Linq dependency, it will be fairly complicated to remove it on our end, so I hope to see this fixed on the Unity side.