I’m happy to see that someone is interessted in the C# wrapper. But first - I didn’t put any work in this for 2 month or so. It probably won’t work out of the box. Also I couldn’t get it to work on windows the last time I tried.
Regarding .net core. It is based on the normal .net framework but the classes used should also be available in .net core. So it would just be building against .net core instead of normal .net.
For serious developments I recommend using C++ or Python with ROS2. You will have to put more work into this wrapper before it can be used properly.