Hello,
it is not clear what precisely you are doing, and what is the precise error message you are getting.

I have made following tests:

1. Using Visual Studio 2019, I created a new project, from template "Console App (.NET Core)". (Note: on my computer at least, this creates a project that has ".NET Core 2.1" as target framework).
2. Using "Manage NuGet Packages", I have installed the package OpcLabs.PicoOpc v1.0.487.
3. I copied/pasted the example code from readme.txt into the Program.cs.
4. I built the project. No errors.
5. I ran the project. It ran without errors.

Please describe in more detailed steps what you are doing and what results you are getting.

Best regards