there is grpc-dotnet, which has more support in Visual Studio for .net CORE then there is C-Core, which supports old .NET FRAMEWORK versions.
I have an Excel-Addin, which is why i am stuck with .NET FRAMEWORK. Can i program a Server Component in grpc-dotnet and consume that from a .NET FRAMEWORK software?
Absolutely. gRPC effectively, is an intermediary between two different solutions or projects, just like JSON, which can be used to share data within the same application or across.