Is there documentation on the use of the JSON library
I just found this, though not much of help in that:
https://docs.ghielectronics.com/software/tinyclr/tutorials/serialization.html?q=json
You could have a look at the full .NET documentation, it is pretty similar to the TinyClr implementation:
https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/overview