Hello,
I've just downloaded your solution and tried to compile both projects and got a nuget package restore error related to the target framework version you're using which is netcoreapp2.0.
Seems latest visual studio 2019 versions do not install .NET Core 2.0 SDK, so my fix was to change the target framework version in both projects to netcoreapp2.1 and now it restores the packages properly. (Of course the recommended approach by now is to target .NET Core 3.0)
My VS 2019 for Windows version is: 16.3.10
My VS 2019 for MAC version is: 8.3.9 (build 2)