This is all and nice, but I can debug a native C plugin. Is this possible for an AOT compiled C# plugin? Or can perhaps the C# plugin be also run with the normale JITting runtime being loaded?
Yes, the AOT compiler can emit debug symbols which point to the C# source files, so depending on your debugger you can get it to work.
I previously had to ship a C#/dotnet library in a native C iOS/Android app. It was a PITA but it worked in the end, and I was even able to debug the C# code in XCode (albeit in a limited fashion).